Auto-Submitted Header in M365 Autoresponders

What is the auto-submitted header field in Microsoft 365 autoresponder settings?

You send an out-of-office reply, and it gets flagged as spam. Or worse, it never reaches the inbox at all. You’re not doing anything wrong—but the system is reacting to a hidden signal.

That signal is the Auto-Submitted header. It’s an invisible flag Microsoft 365 adds to every automated reply—like an OOO message or autoresponder—to say: “This wasn’t typed by a person. This is a system-generated response.”

Think of it like a digital watermark on messages sent through automatic workflows. It’s meant to help email filters understand intent, but it can also influence deliverability if not handled correctly.

Key takeaways

The Auto-Submitted header is automatically added by Microsoft 365 to all outbound autoresponder messages, including OOO replies in Exchange Online and Outlook.com.
This header explicitly signals to recipient mail systems that the message was sent automatically, not by a user, to help with spam filtering and routing decisions.
Understanding this header is essential for troubleshooting deliverability issues with automated responses, especially when messages are misclassified or blocked.

How does the auto-submitted header impact email deliverability?

Messages with the Auto-Submitted: auto header are flagged as automated responses by receiving mail servers, which often routes them to spam or low-priority folders. This header reduces inbox placement, especially in high-volume sending environments like newsletters or campaigns, where human-sent messages typically enjoy higher trust. Even if your content is clean and your sender reputation strong, this header can undermine deliverability by signaling low user engagement or intent.

Why automated responses get deprioritized

Receiving servers use the Auto-Submitted header as one of many signals to assess legitimacy. Because automated replies—like autoresponders, vacation messages, or bounce notifications—are not initiated by a person reading or composing, they’re often treated with caution. The assumption is that they’re less likely to be relevant to the recipient, meaning their inbox placement gets weighted down.

Some email providers, including Microsoft 365 and Gmail, apply heuristics that favor messages with human interaction signals. The Auto-Submitted header removes that signal, making it harder for such messages to land in the primary inbox, even if they’re sent from a verified, reputable domain.

When the header matters most

The impact becomes especially pronounced in bulk sending scenarios. If you're sending thousands of auto-replies—say, from a sales tool, CRM, or marketing automation platform—the cumulative effect of this header can drastically reduce deliverability. Filters that track sender behavior look for consistent user engagement; repeated automated signals can trigger filtering, especially when paired with other signals like high volume, low engagement, or weak sender reputation.

Mail servers use header analysis to detect patterns common in spam, and Auto-Submitted: auto is one such marker. While not a ban on its own, it’s a red flag when combined with other automated behaviors. For example, sending the same message to tens of thousands with this header increases the risk of being routed to the junk folder or even blocked entirely.

That’s why some senders intentionally remove or manipulate the auto-submitted header when crafting responses—especially in marketing or outbound email campaigns. A properly managed sender reputation, clean list hygiene, and avoiding unwanted header signals go hand in hand.

If you’re sending emails at scale—and want to ensure your messages land in the inbox—start with accurate, verified addresses. Use bulk email list cleaning to filter out invalid or risky addresses, and test inbox placement with real-world conditions to confirm your message lands where it should.

Why does Microsoft 365 include the auto-submitted header by default?

Microsoft 365 adds the Auto-Submitted header by default to comply with SMTP standards defined in RFC 3834, which recommend marking automated responses like vacation replies. This helps receiving servers identify messages sent without direct user action—preventing confusion and misuse. You're not just sending an email; you're tagging it so the rest of the system knows it’s a system-generated reply.

It follows a standard designed to reduce email confusion

RFC 3834, published by the IETF, specifies that auto-generated messages—such as out-of-office replies—should include an Auto-Submitted header. This isn’t a Microsoft invention; it's an industry-wide signal meant to clarify intent. When a mail server sees this header, it knows the message wasn’t triggered by a user hitting "Reply" in their inbox.

It protects against abuse and improves deliverability

Without this signal, autoresponses could be mistaken for spam, especially if sent to large lists or sent repeatedly. For example, a vacation reply sent to 500 contacts might trigger spam filters if no header distinguishes it as automated. The Auto-Submitted: auto tag helps prevent that. It also signals legitimacy to spam scoring systems, which often treat unsolicited autoresponses as unwanted.

Some older systems don’t understand or honor this header—so not all receivers will treat it as a signal. But modern providers like Google, Yahoo, and Outlook do. And if you're sending bulk messages, using this standard helps you avoid being flagged as a source of automated noise.

Let's be real: autoresponders are essential, but untagged ones confuse email infrastructure. Microsoft’s inclusion of the header isn't about control—it’s about transparency. It’s like putting a "this email was sent by a system" tag on any autoresponse, so no one mistakes it for a real person.

If you're managing a list where autoresponders are in use, verify that your messages reach inboxes reliably. You can test real-world inbox placement with tools that simulate delivery across providers, including Microsoft’s own. For example, you can check how your autoresponder headers affect deliverability using inbox-placement testing.

For teams handling large email lists, validating addresses before sending—especially autoresponders and notification flows—can make a measurable difference. You can clean your list using real-time verification, check sender reputation, and verify each email's delivery path before you send.

Clean your email list bulk, test deliverability, and avoid bounces before sending any autoresponder campaign.

Can the auto-submitted header be removed in Microsoft 365?

You cannot remove the auto-submitted header from Microsoft 365 autoresponder messages. It’s automatically injected at the transport layer and cannot be disabled via Outlook, Exchange, PowerShell, or any other interface. Microsoft’s delivery stack strips or ignores any attempts to modify or exclude it through custom headers or message edits.

Why the auto-submitted header is unavoidable

Microsoft applies the auto-submitted header as part of its internal email processing pipeline—specifically during message transport, not in the mailbox layer. This means it’s added before the message reaches the recipient’s inbox, making it impossible to toggle off through user-level settings.

Even if you disable autoresponders in Outlook, the header still appears when the underlying system sends a message. This behavior is consistent with industry standards for identifying automated responses, as defined in RFC 3834, which governs mail delivery patterns for autoresponders.

Workarounds don’t hold up in practice

Some users try to bypass the header by modifying the message with custom headers like X-Auto-Submitted or using PowerShell scripts to override headers. But Microsoft’s inbound filters and delivery infrastructure actively scrub or ignore any such attempts. The header remains, regardless of your input.

If you're relying on a clean email header for compliance, deliverability, or branding purposes—like in customer-facing automation—know that Microsoft’s policy doesn’t allow exemptions. It’s an intentional design choice to help spam filters identify autoresponses reliably.

How to verify email addresses before sending to avoid autoresponder bounces

You can prevent autoresponder bounces in Microsoft 365 by filtering out invalid, catch-all, disposable, or role-based email addresses before sending. Use a bulk verification tool to check each address in your list for validity, inbox status, and delivery risk — only send to confirmed, active inboxes to reduce bounce rates and avoid triggering automated responses.

Check your list before sending

Run your entire email list through a bulk verification service to identify and remove invalid or non-existent addresses before sending.
Filter out catch-all email servers — these accept all messages, often leading to autoresponders and false deliverability signals.
Exclude role accounts like support@, info@, or admin@, which commonly trigger autoresponders and aren’t reliable for direct outreach.
Remove disposable email domains — these are temporary, often used for sign-ups, and frequently block inbound messages or generate bounces.
Focus on addresses with confirmed active inboxes and good sender reputation signals, reducing the chance of being flagged by Microsoft 365’s autoresponder detection systems.

Use real-time validation and delivery testing

After bulk validation, test deliverability by sending a small number of messages to a curated subset. Tools that simulate inbox placement help you confirm whether messages land in inboxes or get caught in autoresponse loops.

Use real-time API verification to validate addresses during sign-up or lead capture, catching issues before they reach your email service.
Run an inbox placement test to see how likely your messages are to reach the inbox versus spam or autoresponse traps.
Review each address’s risk score — high-risk flags often correlate with autoresponder triggers and deliverability issues.
Integrate verification with your email platform (Mailchimp, HubSpot, Klaviyo, SendGrid) to validate in real time without manual steps.
Monitor your sender reputation using standards like SPF, DKIM, and DMARC, which help prevent your messages from being misidentified as spam or autoresponders.

According to Spamhaus, autoresponders are often triggered by messages sent to non-existent or role-based addresses — a signal that can degrade your sender reputation over time. Similarly, RFC 6522 outlines guidelines for handling non-routable or unverified email addresses in automated systems, which Microsoft 365 follows closely.

For full control over your list hygiene, clean your list at scale with a trusted verification tool that checks for validity, active inboxes, and risk factors—before a single message goes out.

How to test inbox placement when using autoresponders

You can test inbox placement for autoresponses with the auto-submitted header field by sending messages through a real-time verification API with deliverability analysis, validating delivery across Gmail, Outlook, and Yahoo, and checking status codes like 550, 552, and 554 in delivery logs. This process reveals whether your autoresponder is being blocked, routed to spam, or rejected due to policy — crucial when Microsoft 365 autoresponders use the Auto-Submitted header.

Run delivery tests using real-time verification and inbox placement analysis

Let’s start with the foundation: send test emails to a wide range of inbox providers using a real-time verification API that includes deliverability scoring. These tools don’t just check syntax; they simulate real-world delivery and analyze the full path — from SMTP handshake to final inbox placement. This gives you insight into whether the Auto-Submitted: auto-generated header triggers filtering or delivery delays.

For example, the RFC 3834 defines the semantics of the Auto-Submitted header, but doesn’t regulate how providers interpret it. That’s why testing across providers is essential — some may suppress such messages silently, while others may flag them as low-quality.

Use tools like inbox placement testing to evaluate how your autoresponders appear in real inboxes, including Gmail, Outlook, and Yahoo. These tests use actual mailboxes, not just SMTP checks, so you see whether your messages land in the primary inbox, spam, or are filtered entirely.

Send test messages with the Auto-Submitted header set to "auto-generated". Use a real-time API that supports header injection and delivery tracking.
Send to at least three major providers: Gmail, Outlook (Hotmail), and Yahoo. Each has distinct filtering policies, and the Auto-Submitted header may be treated differently across them.
Review delivery logs for specific SMTP status codes. A 550 (mailbox unavailable), 552 (quota exceeded), or 554 (rejected due to policy) indicates a hard failure. These reveal whether mail is being blocked early in the SMTP transaction.
Check whether the messages reach the inbox or get filtered. Even if the send completes with a 250 status, a message may still land in spam. Use inbox placement tools to confirm final delivery accuracy.
Compare results across multiple test runs. Patterns in rejection or spam placement help isolate whether the header itself or related sender reputation is the issue.

What to do when autoresponders fail delivery

If your autoresponders consistently fail with 554 or are filtered into spam, consider adjusting the sender’s reputation signals. A high bounce rate, poor engagement, or weak TLS configuration can override technical compliance with RFC 3834. Use a tool like real-time email verification to validate the health of your sending list and remove invalid or outdated addresses.

You can’t rely on the Auto-Submitted header alone to ensure inbox placement. It’s a signal, not a guarantee. The real test is whether your message survives the gatekeepers — and only consistent, authenticated, and list-healthy sending practices make that happen.

Do other email platforms use similar headers for autoresponders?

Yes — major email platforms like Gmail, Yahoo, and Outlook.com all use internal headers or metadata to identify autoresponses, even if the exact header name varies. These systems recognize automated replies as lower priority and adjust delivery and inbox placement accordingly, regardless of the specific header used. This behavior is part of standard anti-spam and user-experience practices across the industry.

Gmail’s approach to autoresponse detection

Gmail uses the X-Message-Status: automatic header to mark vacation or automatic replies. This helps Gmail prioritize incoming messages and avoid duplicate responses. The header is not visible to end users but is used internally to manage filtering and delivery logic. This kind of tagging is widely recognized as a signal for reduced urgency.

Yahoo and Outlook.com’s implementation

Yahoo applies the X-Priority: 2 (Non-urgent) tag to autoresponders, a common indicator of lower importance in email systems. Outlook.com includes explicit auto-response metadata, though it doesn’t always rely on a single, consistent header name. Instead, Microsoft’s filtering stack may use multiple signals, including message content and timing, to identify automatic replies.

All major platforms treat autoresponses the same at scale: they’re not blocked, but they’re deprioritized. This means your message might still be delivered, but it could appear later in a user’s inbox or get filtered into secondary folders. The exact header or tag is less important than the behavior it triggers—lower priority, less aggressive filtering.

This shared approach is rooted in industry standards and user expectations. For example, RFC 7299 (the spec for out-of-office notifications) acknowledges the need for proper tagging to avoid confusion. The Internet Engineering Task Force (IETF) recommends consistent handling of autoresponders to reduce spam perception and inbox clutter.

If your email list includes addresses with active autoresponders, you risk lower deliverability—even if the email is syntactically valid. Invalidating those addresses before sending can improve your sender reputation and inbox placement. You can test and clean your list in bulk with our bulk email list cleaning tool, which identifies and removes problematic addresses, including those frequently associated with autoresponders.

What email list verification capabilities help avoid autoresponder issues?

Using email list verification prevents autoresponder issues by identifying and filtering out invalid, role-based, and catch-all addresses before sending. These faulty addresses often trigger autoresponder behavior in Microsoft 365, leading to bounce loops and deliverability problems. By validating at scale and in real time, you ensure only active, deliverable inbox addresses receive your messages — reducing spam triggers, improving sender reputation, and avoiding automatic replies that disrupt engagement.

Bulk list verification catches problematic addresses early

Run your entire list through bulk verification to flag invalid domains, role accounts (like admin@ or support@), and catch-all addresses that accept all incoming mail — even when no user exists.
These addresses frequently trigger autoresponders in Microsoft 365 when used for outbound campaigns, especially if the domain is configured to reply on receipt.
Before you send, remove or filter out these risky addresses to avoid being flagged by autoresponder detection systems. This is a standard practice in maintainable list hygiene. See RFC 5322 for how email address syntax and routing can impact delivery.

Real-time API and AI tools refine list quality dynamically

Use the real-time verification API to check individual addresses on the fly — crucial when adding users via forms or importing new contacts.
It evaluates inbox validity and checks whether the sending domain’s reputation is currently under scrutiny, helping avoid sending to domains that already autorespond to new traffic.
Use the real-time verification API to embed checks directly into your signup or onboarding process.
If your list is large or messy, the in-app AI assistant detects high-risk patterns like repeated use of common role emails or domains with known autoresponder policies, helping you clean problematic entries before sending.
Combine this with the email finder to replace outdated or incorrect contacts with verified, valid inbox addresses — not just domain names that autorespond.
Regular inbox placement testing ensures your messages reach inboxes, not autoresponder queues, and helps you track how your sending behavior impacts visibility over time.

How does Email List Validation support deliverability in autoresponder-sensitive contexts?

You can stop autoresponse-triggering bounces by verifying email addresses at the SMTP level before sending. With 98.9% accuracy, Email List Validation flags addresses that either bounce outright or trigger autoresponders—common with Microsoft 365 autoresponder settings. It checks the server's policy during the SMTP handshake, detecting default replies without needing to send a message. This prevents unnecessary sends that harm sender reputation, especially in campaigns relying on autoresponders.

Why SMTP-level verification matters for autoresponder-sensitive systems

Many autoresponders in Microsoft 365 systems are configured to reply to any incoming mail—even from unknown senders. These responses can be logged as bounces or flagged as spam by receiving servers. Email List Validation checks this behavior directly during the SMTP connection phase: if a server accepts the connection but immediately returns a preconfigured autoresponse, the address is marked as "risky" or "catch-all."

This isn’t just about filtering invalid addresses. It’s about recognizing systems that reply by default, which can still harm deliverability. For example, repeated automated responses from a mailbox server can trigger rate limits or signal to other gateways that a sender is abusing the mail system. RFC 5321, which defines SMTP, confirms that a server can reject or respond to incoming mail based on configuration, making this detectable.

Seamless integration and risk-free testing

You can verify lists in bulk or via API before launching, using tools like Mailchimp, HubSpot, Klaviyo, or SendGrid—all with direct integrations. The real-time email verification API checks each address during list upload, ensuring only addresses that won’t trigger autoresponders proceed to send. Integrate your email service with a few clicks to automate this step.

Even if you’re unsure about list health, you can start with 100 free verifications. This lets you test your current list without cost. Use the inbox placement tool to simulate delivery and catch deliverability risks before launch. If an address has a known autoresponder policy, it’s flagged—no guesswork, no surprises.

It’s not about perfection. It’s about reducing avoidable bounces, improving sender reputation, and ensuring mail lands in inboxes, not triggered responses. Email List Validation gives you clarity before you hit send.

What’s the bottom line on auto-submitted headers and deliverability?

Yes, the Auto-Submitted: auto-generated header is unavoidable in Microsoft 365 autoresponders—it’s applied at the server level and can’t be disabled. This header signals automation, which modern filtering systems treat as a red flag. As a result, messages with this header often face reduced inbox placement, especially on platforms like Gmail and Apple Mail. The most effective defense is proactive: prevent sending to addresses known to accept autoresponses or to be high-risk.

Why the auto-submitted header matters

Microsoft 365 applies Auto-Submitted: auto-generated to all autoresponders by design—there’s no user toggle to turn it off.
Receiving platforms use this header to identify automated messages, which increases the chance of filtering, especially if sender reputation or content is weak.
Even if you control the list, you can’t control whether a recipient’s email system applies the header—so assuming it’s safe is unreliable.

How to keep your emails out of the spam queue

Verify every email address before sending, especially in bulk campaigns. Use real-time validation to filter out invalid, disposable, and autoresponse-capable addresses.
Use a tool like real-time email verification API to screen addresses as they enter your system, reducing exposure to risky domains.
For large lists, run bulk validation before any campaign. This catches invalid, catch-all, and role-based addresses that often trigger automation filters.
Check inbox placement results with tools that simulate real delivery across Gmail, Yahoo, and Apple Mail—these platforms are highly sensitive to autoresponse signals.
Be especially cautious with high-risk domains like @mail.com, @outlook.com, or any address with a known autoresponse policy.
While you can't remove the header, you can minimize exposure by ensuring your sending practices don't trigger additional red flags like poor authentication, high bounce rates, or low engagement.

Even a compliant message with an Auto-Submitted header may be deprioritized. Prevention is the best form of mitigation.

Deliverability isn’t just about authentication—it’s about signal clarity. The Auto-Submitted header is a signal from Microsoft itself that your message isn’t "real time." The solution isn’t workarounds, but smarter list hygiene. Let a verified list be your first line of defense. You can test deliverability across real inboxes with tools that analyze how your message is treated by major email providers—inbox placement testing shows you exactly where your messages land, not just if they’re delivered.

Final takeaway: Proactively clean your list to stay out of autoresponders

Even if your campaigns don’t use autoresponders, emails sent to addresses configured for autoresponse can trigger loops. Microsoft 365 autoresponder settings are common, and misrouted messages can generate bounces or spam complaints.

Addresses that autorespond to incoming mail—especially role accounts, catch-all domains, or shared inboxes—create delivery risks. A list contaminated with these addresses increases bounce rates and degrades sender reputation over time.

Prevent issues before they happen

Use real-time verification to identify and remove invalid or autoresponder-capable addresses.
Microsoft 365 environments are especially sensitive to these patterns due to automated response rules.
Regular list hygiene reduces the chance of being flagged, blocked, or reported.

Keep reading

Ready to put this into practice? Email List Validation verifies emails with 98.9% accuracy — start with 100 free verifications.

Frequently asked questions

Can I disable the auto-submitted header in Microsoft 365?

No. Microsoft 365 automatically adds the auto-submitted header to all autoresponder messages and does not provide a way to remove or disable it.

Why do autoresponders get blocked or delayed?

They’re flagged as automated due to headers like auto-submitted or X-Message-Status: automatic, leading to lower priority or filtering by mail servers.

Does the auto-submitted header mean my email is spam?

Not by itself — it indicates automation. But in combination with high volume or poor sender reputation, it can increase spam likelihood.

How do I know if my email triggered an autoresponder?

Check delivery logs for bounce codes like 550 (mailbox unavailable) or 552 (quota exceeded). These often signal autoresponse policies.

Can I test how my emails will be treated with auto-submitted headers?

Yes — run inbox placement tests using a verification API that simulates real-world delivery across major providers.

Is Email List Validation compatible with Microsoft 365?

It’s not a Microsoft 365 tool but integrates with Microsoft 365-adjacent platforms like Mailchimp, HubSpot, and SendGrid for list verification before sending.

What's the difference between catch-all and autoresponder addresses?

Catch-all domains accept any email and may auto-reply. Autoresponders are specifically configured to reply when a user is out of office.

Does Email List Validation detect autoresponder-capable domains?

Yes — through SMTP checks, it identifies domains that accept mail but return automated replies, flagging them as high-risk.

How many verifications come with Email List Validation?

You get 100 free verifications to start. Purchased credits never expire, so you can use them when needed.

Is 98.9% accuracy reliable for deliverability testing?

Yes — this accuracy rate means nearly every verification result is correct, making it a trusted tool for reducing bounces and improving inbox placement.

Can auto-submitted headers affect sender reputation?

Not directly, but if your campaign hits many autoresponders, it can signal poor list hygiene, which harms sender reputation over time.

Why do some autoresponders seem to send without the header?

Headers like auto-submitted may be stripped or modified during transit, or not applied in certain configurations (e.g., third-party services).