How to check what Message Transfer Agent is used on the server with Plesk and how to switch it?

1. Log in to Plesk GUI

2. Go to Tools & Settings > Services Management:

3. Find SMTP Server line. Depending on the installed MTA it will be:

   SMTP Server (Postfix)
   OR
   SMTP Server (QMail)

1. Connect to the server via SSH

2. Execute the following command:

   # plesk sbin mailmng-server –features | grep SMTP_Server

   Depending on the installed MTA, the output will be:

   # plesk sbin mailmng-server –features | grep SMTP_Server
   $features[‘SMTP_Server’] = “Postfix”;
   $features[‘SMTP_Server_package’] = “postfix”;

   OR

   # plesk sbin mailmng-server –features | grep SMTP_Server
   $features[‘SMTP_Server’] = “QMail”;
   $features[‘SMTP_Server_package’] = “psa-qmail”;

Note: Before switching the MTA, it is recommended to wait until all queued emails are delivered.

1. Log in to Plesk GUI

2. Go to Tools & Settings > Services Management

3. Stop the service SMTP Server

4. Go to Tools & Settings > Updates and Upgrades > Add/Remove Components > Mail Hosting > SMTP servers.

5. Select the necessary SMTP server – QMail or Postfix.

6. Click Continue > Install

Note: Before switching the MTA, it is recommended to wait until all queued emails are delivered.

1. Connect to the server via SSH

2. Stop the Mail service:

   # plesk sbin mailmng-service –stop-service

3. Make sure that there aren’t processes binding port 25:

   # lsof -i :25
   (Empty Output)

   In case any process is returned by the previous command, run the following command to kill running processes:

   # lsof -i :25 | grep LISTEN | awk ‘{print $2}’ | sort | uniq | xargs kill

4. Install the necessary SMTP server:

   • Postfix

     # plesk installer –select-release-current –install-component postfix

   • QMail

     # plesk installer –select-release-current –install-component qmail

   Also, it is possible to run Plesk installer and select the necessary SMTP server in Mail Hosting section:

   # plesk installer

1. Log in to Plesk GUI

2. Go to Tools & Settings > Mail Server Settings > Mail Queue tab > Clear

1. Connect to the server via SSH

2. Clear the mail queue according to the installed MTA:

   • For QMail:

     # kill -ALRM pidof qmail-send

   • For Postfix:

     # postqueue -f