Fix SMTP Error 451 (Temporary local problem – please try later)

A problem that many server administrators face at the moment, is about a less common error SMTP that appears at the time of sending an email message. Fix SMTP Error 451.

The causes of this error can be multiple, which is why it is good to investigate all the possible causes. In my case, in the first part of the tutorial I refer to a particular case.

SMTP Error 451 (Temporary local problem – please try later)

It is not a hacking or a problem caused by a configuration error. error SMTP 451 appears especially on operating systems CentOS cu VestaCP Installed, and the error log looks like this:

2020-07-03 11:17:11 Tainted filename for search: '/etc/exim/domains/domain.com/aliases'
2020-07-03 11:17:11 H=(costa.onlymale.live) [104.140.84.7] F=<15304-3132-5583-4006-name=domain.com@mail.onlymale.live> temporarily rejected RCPT <name@domain.com>: failed to expand "${extract{1}{:}{${lookup{$local_part@$domain}lsearch{/etc/exim/domains/$domain/aliases}}}}": NULL

I don't know if the problem is for the servers that have cPanel, but on Vestacp Sure is a problem. Basically no user can send email anymore, even if the connection to the email server seemed to be okay.

The error appears after a Configuration incompatibilities In the latest EXIM update for CentOS (exim 4.94-1.el7), and so far there is no “fix” to solve this problem. However, there is a very simple solution.

How we solve the SMTP 451 error (temporary Local Problem – please try later)

Return to the previous version of EXIM (downgrade) is the most handy solution for email administrators with vestacp.

1. We authenticate on Linux via SSH and we execute the command lines through which we download and install the old version of EXIM.

wget https://stealthsettings.com/download/exim-4.93-3.el7.x86_64.rpm
rpm -Uvh --oldpackage exim-4.93-3.el7.x86_64.rpm

Output:

2. Restart “exim” and be careful that the services “clamd” and “spamassassin” to run.

What I have presented above is a particular case, but this type of error can be generated by various temporary causes that you must take into account and which you must investigate. Such as, a problem at the recipient's e-mail server or overcoming the message limit shipped within a period of time.

Other causes from which SMTP Error 451 may be present

→ The SMTP 451 error may also indicate that the user has exceeded the limits set on the email server for sending emails. The email server will not allow the user to send more emails than the set limits. These limits are set as daily or hourly limits to restrict the abusive behavior of users.

→ The recipient's email server is overloaded with messages or encounters performance problems. It has a very large Load and cannot process the requests for inputs;

→ The recipient's e-mail server is in the process of maintenance. It is very possible that the specific and / or connectivity services may be stopped;

→ There is a temporary problem with the network or connection to the recipient's email server.