/usr/local/cpanel/3rdparty/mailman/data/master-qrunner.pid

PID unreadable in: /usr/local/cpanel/3rdparty/mailman/data/master-qrunner.pid [Errno 2] No such file or directory: '/usr/local/cpanel/3rdparty/mailman/data/master-qrunner.pid' Is qrunner even running? Shutting down Mailman's master qrunner mailmanctl: no process killed when trying to install Neo-mail from Tweak settings

Sol:

$>/scripts/reinstallmailman

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You can also use

$>/scripts/mailman212

to completly upgrade it along with necessary cpanel upgrades.