550 5.7.708 / 5.7.705: Tenant or IP blocked from sending

Microsoft 365SMTP

The error usually looks like this:

550 5.7.708 Service unavailable. Access denied, traffic not accepted from this IP.

What it means

Microsoft 365 has restricted sending from your organization or IP address, usually because of suspicious or high-volume outbound email.

Common causes

  • Your organization has sent a large amount of spam (5.7.705, tenant has exceeded threshold).
  • A new organization’s outbound mail looks suspicious (5.7.708).

How to fix it

  1. Check for compromised accounts and reset their passwords.
  2. Contact Microsoft support to have the restriction reviewed.

Tools to help diagnose it

Email blacklist checker

Check whether a mail server IP address or domain is listed on common email blocklists

Email header analyzer

Trace your email’s delivery path and check SPF, DKIM, and DMARC authentication results

A free tool provided by Auth-Email

Auth-Email makes your Gmail, Outlook, or other OAuth 2.0 email account available to any IMAP, POP3, or SMTP email client — no app passwords or special configuration needed.

Read the docsTry Auth-Email →

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