5.7.506 Microsoft bounce: bad helo name
What 5.7.506 means
Your sending server introduced itself with the name of the server it was connecting to, which Exchange Online treats as spambot behaviour.
Message text
Access Denied, Bad HELO
Common causes of 5.7.506
- Sending server uses the recipient's server name in HELO/EHLO instead of its own fully qualified domain name
How to fix 5.7.506
- Set the sending server's HELO/EHLO name to its own fully qualified domain name.
- Make sure that name matches its reverse DNS entry, checked with reverse DNS lookup.
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How to read 5.7.506
The second part, 5.7.506, is an enhanced status code (RFC 3463 §2) written class.subject.detail. Class 5 is a Permanent failure (5xx): the command was rejected and the sender should not repeat it unchanged (RFC 5321 §4.2.1; RFC 3463 §2).. Subject 7 is security or policy: authentication, authorization or policy refused the message. The detail number refines the subject, and providers may define details of their own, which is why one code can read differently at Gmail, Microsoft and Yahoo.
Do not keep resending the same message: a permanent failure repeats until the cause is fixed. Correct the cause, then send a new message.
Official source: learn.microsoft.com. Last verified 2026-10-20.
Related guides
- How to create an SPF record (syntax and examples)
- How DKIM works and how to publish a DKIM record
- How to set up a DMARC record, from p=none to p=reject
Related codes
- 5.7.0 SMTP: security status
- 5.7.1 SMTP: delivery not authorized
- 5.7.23 SMTP: SPF validation failed
- 5.7.25 SMTP: reverse DNS failed
- 5.7.26 SMTP: authentication failed
- 5.7.27 SMTP: sender has null MX
FAQ
What does 5.7.506 mean?
Your sending server introduced itself with the name of the server it was connecting to, which Exchange Online treats as spambot behaviour. This is a permanent failure.
How do I fix 5.7.506?
Set the sending server's HELO/EHLO name to its own fully qualified domain name. Make sure that name matches its reverse DNS entry, checked with reverse DNS lookup.
Is 5.7.506 permanent, and should I retry?
5.7.506 is a permanent failure, so retrying the same message will fail again. Fix the cause first, then send a new message.