SMTP 550 5.7.515: inspect Outlook’s required authentication level

Define the decision

The error is associated with Outlook consumer sender requirements. It is not evidence that your Microsoft 365 mailbox password is wrong. Confirm the rejecting host and response text before choosing a repair.

Work through the procedure

1. Save the complete rejection including the named sending domain.
2. Inspect SPF and DKIM results on the same production sending path.
3. Compare passing identities with the visible From domain for DMARC.
4. Correct the sender-side configuration and run a controlled test to the affected recipient service.

Worked example

The following is a synthetic example for this procedure, not a customer result or performance benchmark.

Response: 550 5.7.515, sending domain does not meet required authentication level
Connection already submitted successfully
Investigation: domain authentication and alignment
Unhelpful action: repeatedly reconnecting the mailbox without changing the failing identity

Read the result

A DNS record being present is not the same as a message passing authentication. A stale signer, unrelated provider domain or missing legitimate sender can explain the difference.

Check before moving on

1. Use a new message after the correction.
2. Confirm both the envelope and signing identities actually used.

Limits and next action

Review Microsoft’s current support page for the complete requirements. Do not infer the cause solely from a truncated numeric code or treat a successful retest as an inbox guarantee.

Source: Microsoft: fix Outlook 550 5.7.515