Find your mbox files
ls -la /usr/local/cpanel/3rdparty/mailman/archives/private/my1_lists.domain.com.mbox/my1_lists.domain.com.mbox ls -la /usr/local/cpanel/3rdparty/mailman/archives/private/my2_lists.domain.com.mbox/my2_lists.domain.com.mbox
Backup *.mbox files if needed and empty them:
truncate -s 0 /usr/local/cpanel/3rdparty/mailman/archives/private/my1_lists.domain.com.mbox/my1_lists.domain.com.mbox truncate -s 0 /usr/local/cpanel/3rdparty/mailman/archives/private/my2_lists.domain.com.mbox/my2_lists.domain.com.mbox
Go to bin/ folder and wipe as following:
cd /usr/local/cpanel/3rdparty/mailman/bin ./arch --wipe my1_lists.domain.com ./arch --wipe my2_lists.domain.com
To get the changes reflected in cPanel and wipe cache run next:
/scripts/update_mailman_cache