Remove MailMan from Plesk
Login to your Dedicated-Virtual Server using SSH as the root user. Now lets run the command to find what version of mailman is currently installed.
You should find results similar to the following
mailman-2.1.1-5
mailman-2.1.1-7.legacy
Now we will use rpm to uninstall
rpm -e mailman-2.1.1-5
rpm -e mailman-2.1.1-7.legacy
Enable Mailman in Plesk
The following steps will show you how to enable Mailman.
1. Login to Plesk.
2. Click on Server.
3. Click on Set Up Mailman.
4. Configure Mailman by providing the Mailing list administrator’s email and password.
5. Once you hit OK you should be taken back to the server page with the message letting you know that the Mailman icon will no longer be accessible.
For information on using Mailman please visit http://www.gnu.org/software/mailman/index.html
Bug in Mailman
Bug in Mailman version 2.1.9.cp2
We’re sorry, we hit a bug! Please inform the webmaster for this site of this problem. Printing of traceback and other system information has been explicitly inhibited, but the webmaster can find this information in the Mailman error logs.
One of the reason for the issue is that the folders in /usr/local/cpanel/3rdparty/mailman is not having sufficient permission. You can perform the following steps to fix the issue:
Go to /usr/local/cpanel/3rdparty/mailman and check the permission of all the folders.
$ ls -al /usr/local/cpanel/3rdparty/mailman
And then Try.
Now the permission of folders must have changed. Check if this has fixed the issue.
If not, you can try running the fixmailman script in the server at /scripts.