If you gets an Internal Server Error while accessing : http://example.com/mailman/admin/, you may need to fix some permission problems in the mailman.---
chmod 02755 -R /usr/local/cpanel/3rdparty/mailman
/usr/local/cpanel/3rdpart/mailman/bin/check_perms -f
chmod 02775 -R /usr/local/cpanel/3rdparty/mailman/logs
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