Unable to access Webmail service on a Plesk server; the following error is shown on the web browser: 500 Internal Error

Symptoms

• Unable to access Webmail service on a Plesk server; the following error is shown on the web browser:

  500 external Error

• The following error is found in/var/log/httpd/error_log:

  [fcgid:warn] [pid 23193:tid 139691422762752] (104)Connection reset by peer: [client 10.0.113.2:55064] mod_fcgid: error reading data from FastCGI server
  [core:error] [pid 23193:tid 139691422762752] [client 10.0.113.2:55064] End of script output before headers: index.php

• In /var/log/messages or /var/log/syslogfollowing error is found:

  cgi_wrapper[5905]: can not find appropriate version of php ~ plesk-php73-fastcgi' in/etc/psa/php_versions.json'

Cause

The plesk-php73-fastcgi version was manually removed from the server without its dependencies. Without it, the webmail service could not be served, hence the error.

Resolution

1. Log into Plesk

2. Go to Tools and Setings > Updates > Add/Remove Components > Web Hosting > PHP interpreter versions and install version 7.3

3. Once done Connect to the server via SSH and re-read the PHP handlers:

   # /usr/local/psa/admin/bin/php_handlers_control --reread