[CentOS] Mail server with both postfix and sendmail installed, active MTA gets switched.

Sat Jan 5 21:15:35 UTC 2019
Lamar Owen <lowen at pari.edu>

On 1/5/19 2:18 AM, Gordon Messmer wrote:
> On 1/4/19 8:29 PM, Lamar Owen wrote:
>> I have had updates twice now switch the active MTA to sendmail, and I 
>> have to manually 'systemctl disable sendmail; systemctl stop 
>> sendmail' and 'systemctl enable postfix;systemctl start postfix' 
>> afterwards.
> Run "systemctl mask sendmail" as well.  That should permanently 
> disable the service.
Worthwhile thing to do; still curious about what caused it, but if this 
will lock it out.....

>> I am trying to find out what package update caused this to switch; or 
>> which logfile to look at to show me the systemctl messages that show 
>> the enable/disable sequence and points me to the correct package to 
>> file the bug against.
> ...
> If the problem is a trigger on the sendmail package, it could run 
> without any changes to the sendmail package itself.
Ah, yes, indeed. Only three packages are output: sendmail itself, 
postfix, and the third party software; postfix did get an update 
recently, and after checking to see I didn't reboot after that update.  
And the postfix scriptlets do twiddle with alternatives, using the 
--initscripts command to alternatives; and this is what I believe did me in.

So, it seems as part of my setup that I failed to set the alternatives 
properly, and that has been corrected, as well as setting 'systemctl 
mask sendmail' so we'll see how that rides...

Thanks, Gordon!