The recipient cannot be verified. Please check all recipients of this 550 message to verify they are valid

If you are receiving the following error;

PERM_FAILURE: SMTP Error (state 13): 550-"The recipient cannot be verified. Please check all recipients of this
550 message to verify they are valid."

SOLUTION:

First you need to check the corresponding Domain name in the file '/etc/valiases'.

root@f ~] cat /etc/valiases/domainname
*: username@domainname

Here 'username@domainname' indicates an added email account.

You need to change the username only instead of giving 'username@domainname'. That is;

root@f ~] cat /etc/valiases/domainname
*: username

Here the entry username (without the domain name) indicates the default account.

Then Restart the exim mail service.

root@f ~] /etc/init.d/exim restart