SMTP 250 OK vs 251 User Not Local
Both SMTP 250 (OK) and 251 (User Not Local) belong to the 2xx Positive Completion category. 250 indicates that the requested mail action has been completed successfully. This is the most common positive response in SMTP, returned after HELO/EHLO, MAIL FROM, RCPT TO, and DATA completion. Meanwhile, 251 means that the recipient is not local to the server, but it will forward the message to the specified forwarding address. The server acts as a relay for this recipient.
Description
The requested mail action has been completed successfully. This is the most common positive response in SMTP, returned after HELO/EHLO, MAIL FROM, RCPT TO, and DATA completion.
When You See It
After nearly every successful SMTP command — greeting, specifying sender, adding recipients, or completing message delivery. This is the standard success confirmation.
How to Fix
No fix needed — the command was accepted. If a command that should succeed returns a different code, check the command syntax and server policies.
Description
The recipient is not local to the server, but it will forward the message to the specified forwarding address. The server acts as a relay for this recipient.
When You See It
When sending to a recipient whose mailbox is hosted on a different server. The current server knows the forwarding address and will relay the message on your behalf.
How to Fix
No fix needed — the message will be forwarded automatically. To avoid relaying, send directly to the address provided in the server's response.
Key Differences
SMTP 250: The requested mail action has been completed successfully. This is the most common positive response in SMTP, returned after HELO/EHLO, MAIL FROM, RCPT TO, and DATA completion.
SMTP 251: The recipient is not local to the server, but it will forward the message to the specified forwarding address. The server acts as a relay for this recipient.
You encounter 250 when after nearly every successful SMTP command — greeting, specifying sender, adding recipients, or completing message delivery. This is the standard success confirmation.
You encounter 251 when when sending to a recipient whose mailbox is hosted on a different server. The current server knows the forwarding address and will relay the message on your behalf.
When to Use Which
For 250 (OK): No fix needed — the command was accepted. If a command that should succeed returns a different code, check the command syntax and server policies. For 251 (User Not Local): No fix needed — the message will be forwarded automatically. To avoid relaying, send directly to the address provided in the server's response.