Investigate mail auth for Salt 3006.17

[JacobCoffee]

From #618(ee):

The salt-master upgrading to 3006.17 via unattended upgrades brought the new default minimum authentication setting

Remediation:

I set a more permissive authentication mechanism temporarily on the salt-master to override the new default (this is only necessary currently for the mail host which runs salt 2018 series.

ee@salt:~$ sudo cat /etc/salt/master.d/hold-back.conf
minimum_auth_version: 0

[JacobCoffee]

I am wondering if we can use https://docs.saltproject.io/salt/user-guide/en/latest/topics/salt-ssh.html just for mail, reading the docs i think that would let us go "minion-less" on the old OS so we can bump that minimum_auth_version back to normal?

[JacobCoffee]

Or we could run an old salt-master just for mail 😅
more seriously, I have pinged mark to see status on the new 24.04 mail droplet we set up to put a higher prio on migrating asap