Microsoft Outlook - Why automatic replies (out of office) don't always arrive

David

Updated October 27, 2026 16:23

Microsoft 365 sends automatic replies on a best-effort basis. Microsoft sends them, but the recipient's mail system decides whether to deliver them.

In short: if your out-of-office reaches some outside senders and not others, your settings are working. The difference is how the receiving system treats automated mail.

Why do my replies reach Microsoft 365 users but not Gmail or some companies?

Microsoft sends automatic replies differently from normal email. They go out from a separate, lower-priority pool of Microsoft servers, and they carry a blank return address. Gmail and security gateways like Proofpoint, Mimecast and OpenText often score that combination as suspicious. Between two Microsoft 365 organizations, the message stays on Microsoft's network, so those filters never see it.

Why would a filter block a legitimate out-of-office?

Because spammers abuse auto-replies. When spam is sent with a forged sender, every out-of-office it triggers lands on an innocent person. This is called backscatter. Many security platforms block or quarantine unexpected auto-replies to protect their users from it, and some only accept them when they match an email their own user recently sent.

Is something wrong with my mailbox?

Usually not. If your reply reaches some outside senders and not others, your settings are working. The difference is on the receiving end.

I tested it twice and only got one reply. Why?

Microsoft sends one automatic reply per sender for each out-of-office period. To test again, use a different outside address, or turn automatic replies off and on.

Why didn't anyone get a reply after I set up forwarding?

When a mailbox forwards all its mail to another address, Microsoft does not generate automatic replies. Contact us if you need both at once and we'll set it up another way.

Can I see who received my automatic reply?

No. Automatic replies are not saved in Sent Items. We can check delivery for a specific sender through Microsoft's message trace if needed.

Can you make sure every reply gets delivered?

No provider can. We make sure your domain is properly authenticated, which gives replies the best possible chance. Beyond that, the recipient's spam settings decide. If a key contact never receives your replies, their IT team can allow-list your domain.

What should I do for important absences?

Name a backup contact or shared mailbox in your reply, and tell key clients before you leave.
Update your voicemail greeting and, if relevant, your website.
Colleagues on Microsoft 365 will see your out-of-office notice in Outlook as soon as they start writing to you.