Unable to send mail with sendmail in Plesk: sendmail unsuccessfully finished with exitcode 70

Symptoms

• Unable to send mail message via sendmail command line utility:

  # echo "Subject: sendmail test" | sendmail -v johndoe@example.com
  plesk sendmail[21306]: my_popen(): execve(/usr/lib64/plesk-9.0/sendmail/sendmail.postfix) failed: No such file or directory [2]
  plesk sendmail[21306]: Unable to execute MTA
  plesk sendmail[21305]: sendmail unsuccessfully finished with exitcode 70

  ---

  CONFIG_TEXT: /usr/sbin/sendmail: 1: /usr/sbin/sendmail: Syntax error: Unterminated quoted string

  ---

  CONFIG_TEXT: /usr/sbin/sendmail: cannot execute binary file: Exec format error

  ---

  CONFIG_TEXT: plesk sendmail[20188]: cannot create temporary file - (13) Permission denied
  plesk sendmail[20188]: Unable to save stdin content to temporary file

• The same error can be found on /var/log/maillog file.

Cause

File/usr/lib64/plesk-9.0/sendmail/sendmail.postfix is missing or corrupted.

Resolution

1. Determine what mail server installed: Plesk > Tools & Settings > Mail Server Settings:
   
   

2. Connect to the server via SSH;

3. Download and reinstall suitable for environment and installed Plesk version package from Plesk repository:
   "plesk-mail-pc-driver" (for Postfix mail server)
   "plesk-mail-qc-driver" (for Qmail mail server) 

   example for Debian-based OS:

   # wget http://autoinstall.plesk.com/PSA_18.0.31/dist-deb-Ubuntu-20.04-x86_64/opt/maildrivers/plesk-mail-pc-driver_18.0-v.ubuntu.20.04+p18.0.31.2+t201127.1705_amd64.deb

   Remove the current package:

   # dpkg -P --force-all plesk-mail-pc-driver

   Install the downloaded one:

   # dpkg -i plesk-mail-pc-driver_18.0-v.ubuntu.20.04+p18.0.31.2+t201127.1705_amd64.deb

   example for RedHat-based OS:

   # wget http://autoinstall.plesk.com/PSA_18.0.31/dist-rpm-CentOS-8-x86_64/opt/maildrivers/plesk-mail-pc-driver

   Remove the current package:

   # rpm -ev plesk-mail-pc-driver

   Install the downloaded one:

   # rpm -ivh plesk-mail-pc-driver-18.0-2.centos.8+p18.0.31.2+t201127.1705.x86_64.rpm