Microsoft mail servers 550 5.7.64
Connector configuration
Connector configuration means the receiving provider rejected the message for a provider-specific reason. Use the diagnostic text before deciding on retries or suppression.
Decision
Do not retry unchanged. Fix the sender setup first.
Confidence: high. Recipient validity: unknown.
Match this reply
- SMTP stage
- MAIL FROM
- Endpoint
- Inbound MX
TenantAttributionRelay Access DeniedStart here
- 1
Read the full SMTP diagnostic text, not only the numeric reply code.
- 2
Identify the provider, SMTP stage, and any provider token before deciding whether to retry or suppress.
Confirm the cause
- Match provider, SMTP stage, endpoint, reply code, enhanced code, and diagnostic text.
- Run the sender, recipient, DNS, and content checks that match the diagnostic wording.
- Test with one recipient before retrying bulk traffic.
App handling
- Treat this as a sender setup incident, not a bad recipient.
- Hold similar mail for the same sender domain or provider until the fix is verified.
- Retry after a fresh single-recipient test succeeds.
Avoid
- Do not retry unchanged in a loop.
- Do not suppress the recipient unless the text explicitly says the mailbox is invalid.
- Do not treat a permanent SMTP code as proof that the address is bad; policy and routing failures can also be permanent.
Common causes
- The provider-specific diagnostic text matches this class of failure.
- The same SMTP code may have another meaning when the provider, stage, or endpoint differs.
- Sender setup, recipient status, and provider policy should all be checked before taking irreversible action.
Developer details
Fields to log
raw SMTP replyremote MX or hostSMTP stagereply codeenhanced codeprovidermatched rule idrecipientsending domaindecisiontimestamp
Classifier evidence
- Specific cause
- tenant attribution failed
- Evidence
- official