Mail forwarding or website mail form does not work on Plesk server: Unable to execute MTA: Permission denied

Symptoms

Mail forwarding or mailing form on a website hosted in Plesk does not work with the following errors in /var/log/maillog file:

sendmail[16679]: my_popen(): execve(/usr/lib/plesk-9.0/sendmail/sendmail.postfix) failed: Permission denied [13] sendmail[16679]: Unable to execute MTA

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sendmail[2118]: Unable to save stdin content to temporary file
sendmail[2120]: cannot create temporary file - (13) Permission denied

Cause

Incorrect permissions/ownerships on the Sendmail binary files.

Resolution

1. Connect to the server via SSH.

2. Set correct permissions and ownerships for Sendmail binary files:

   • on CentOS/RHEL-based distributions:

     # chown root:root /usr/lib64/plesk-9.0/sendmail/sendmail.postfix && chmod 755 /usr/lib64/plesk-9.0/sendmail/sendmail.postfix
     # chown root:root /usr/lib64/plesk-9.0/postfix-sendmail-wrapper && chmod 4755 /usr/lib64/plesk-9.0/postfix-sendmail-wrapper

   • on Debian/Ubuntu-based distributions:

     # chown root:root /usr/lib/plesk-9.0/sendmail/sendmail.postfix && chmod 755 /usr/lib/plesk-9.0/sendmail/sendmail.postfix
     # chown root:root /usr/lib/plesk-9.0/postfix-sendmail-wrapper && chmod 4755 /usr/lib/plesk-9.0/postfix-sendmail-wrapper