5.x.x permanent failure
SMTP Error Code 501: Meaning, Causes and How to Fix It
SMTP 501 is a permanent failure.
A syntax error in the command arguments, almost always a malformed or invalid address in the envelope or headers. It stays permanent until the address is corrected.
- Class
- 5xx permanent
- Bounce type
- Hard bounce
- Highest severity
- Low
- Responses on record
- 5
GMX
Orange
Outlook
QQ
Yahoo IncSMTP 501 responses from email providers
How mailbox providers phrase a 501. Open a provider for the full text, severity and fix for every variation.
SMTP 501 questions
›Is SMTP 501 a hard bounce or a soft bounce?
It is a permanent failure, so a hard bounce. The receiving server will not accept the same message on a retry, and the address or the sending problem has to be fixed before you resend.
›What causes an SMTP 501 error?
A syntax error in the command arguments, almost always a malformed or invalid address in the envelope or headers. It stays permanent until the address is corrected. The exact reason varies by receiver, which is why this page lists the specific 501 responses recorded for GMX, Orange, Outlook, QQ, Yahoo Inc.
›How do I fix an SMTP 501 bounce?
Read the enhanced status code and the message text, not just the number. Wording that names the recipient (user unknown, mailbox unavailable) means correct or remove the address. Wording that names authentication or reputation (SPF, DKIM, DMARC, blocklist) means fix that on the sending side, or clear the listing. Every response on this page has its own guidance.