cPanel - SMTP Error (451): Failed to set sender



Error:

When you try to send mails from any email client using cPanel, you may see the following error flashed

SMTP Error (451): Failed to set sender "test@example.com"  (Temporary local problem - please try later)

or

code 451 response temporary local problem please try later

Solution:

Let you are trying to send mail from "test1@yourdomain.com" to "test@example.com"

If "test1@yourdomain.com" is using local mail server, the command given below must display "yourdomain.com" as result.

# cat /etc/localdomains | grep yourdomain.com
 
If the output is null, add an entry for "yourdomain.com" in /etc/localdomains.

Also remove the entry of "yourdomain.com" in /etc/remotedomains if there exists one.