455: parameters cannot be handled now
The server cannot handle one of the parameters given with MAIL FROM or RCPT TO at the moment, and asks the sender to try again later.
- Standard
- Provider
- Temporary (4xx)
- Class
- Sources checked
- Author
At a glance
- Code
- 455
- Provider
- Standard SMTP codes
- Temporary or permanent
- TemporaryThe sending server keeps the message and tries again later.
- Who has to act
- The sender. The fix is on the sending side: your domain, your server or your list.
- What the server says
455 Server unable to accommodate parameters
What it means
RFC 5321 defines 455 for a server that is temporarily unable to accommodate one or more parameters on a MAIL FROM or RCPT TO command, when the parameter's own specification does not call for a different code. The parameters are the extension options a client can add to those commands, such as a declared message size or a request for delivery notices. Its permanent counterpart is 555. As a 4xx reply it allows a retry later. It is uncommon in everyday mail traffic.
Common causes
- An extension option on MAIL FROM or RCPT TO that the server cannot handle right now.
- A condition on the server that makes the requested option temporarily impossible.
How to fix it
- 01Let the sending server retry.
- 02Read the reply text for the parameter concerned.
- 03If it keeps happening, resend without that option.
Sources
What this page rests on, checked on 20 Oct 2026. The explanation is ours; the reply text is the server's.
Related codes
- 555Parameters not recognised.The server does not recognise, or does not implement, a parameter given with MAIL FROM or RCPT TO, so that command failed.
- 5.5.4Invalid command arguments.A valid SMTP command was sent with an argument the server does not accept, because the value was out of range or named a feature it does not know.
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