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550 5.7.708: Traffic not accepted from this IP (Microsoft 365)

Microsoft 365 has restricted your tenant's outbound mail because most of its traffic looks suspicious.

Bounce type
Hard bounce (permanent)
What to do
Pause sending and repair reputation
Returned by
Microsoft (Outlook.com, Microsoft 365)

What 550 5.7.708 means

Microsoft documents 5.7.705 ('Access denied, tenant has exceeded threshold') and 5.7.708 ('Access denied, traffic not accepted from this IP') together: most of the traffic from the sending Microsoft 365 tenant was detected as suspicious, so Microsoft banned the tenant's sending ability.

This comes from your own Microsoft 365 tenant, not the recipient. It's common with brand-new or trial tenants that start sending outreach volume immediately, which is exactly what Microsoft's outbound filters look for.

What the bounce looks like

The wording providers document for this code. Your bounce may add an IP address, a session ID or a help link after it.

Microsoft
550 5.7.708 Access denied, traffic not accepted from this IP
Microsoft
550 5.7.705 Access denied, tenant has exceeded threshold

Why cold emailers see 550 5.7.708

  • A new or trial Microsoft 365 tenant sending cold email at volume from day one.
  • A compromised mailbox in the tenant sending spam.
  • Many mailboxes in one tenant sending similar messages to external recipients.

How to fix 550 5.7.708

  1. Stop all outbound campaigns from the tenant.
  2. Check for compromised accounts and reset credentials if anything looks wrong.
  3. Contact Microsoft support through your admin center; Microsoft says the ban is lifted through support once issues are resolved.
  4. When sending resumes, start with low volume and normal human-like patterns.

Retry or suppress?

Don't suppress the recipients. Nothing will send from this tenant until Microsoft lifts the restriction.

Reading the code

The basic code 550 means "Mailbox unavailable or message refused (permanent)" under RFC 5321. In 5.7.708, the 5 is the class (permanent failure) and the 7 is the subject (security or policy). The detail number 708 isn't in the RFC 3463 / IANA registry; it's specific to the provider, so the text after the code carries the meaning.

Class 5
Permanent failure
Resending the same message won't work. Something about the message, the recipient or the sender has to change first.
Subject 7
Security or policy
A security or policy decision: spam filtering, authentication, blocklists, permissions.
Detail 5.7.708
Provider-specific

Check the rest of your setup

Paste the headers of a message that did get through into the email header analyzer to confirm SPF, DKIM and DMARC pass, and check your domain with the SPF, DKIM & DMARC checker. The deliverability checklist covers the rest of a healthy sending setup.

Got a different bounce? Paste it into the SMTP error code lookup to decode it.

FAQ

Is 550 5.7.708 a hard bounce or a soft bounce?

550 5.7.708 is a permanent failure (a hard bounce): the receiving server won't accept this message if you send it again unchanged. But the cause is not the recipient's address, so treat it differently from a 'user unknown' bounce.

Should I remove the contact after a 550 5.7.708 bounce?

No. Don't suppress the recipients. Nothing will send from this tenant until Microsoft lifts the restriction.

What does 5.7.708 mean in the error code?

In 5.7.708, the 5 is the class (permanent failure) and the 7 is the subject (security or policy). The detail number 708 isn't in the RFC 3463 / IANA registry; it's specific to the provider, so the text after the code carries the meaning.

Related SMTP codes

See all SMTP error codes

Sources

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Clement reads the bounces that land in your Gmail and SMTP inboxes and tells dead addresses apart from policy blocks: it suppresses the first across every campaign and keeps the contact on the second, so you don't have to decode bounces by hand.

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