Chris Knadle wrote:
> On Friday 08 October 2010 17:09:53 Ron Guerin wrote:
>
>> Also, MTAs do not play nice together willingly (even if it's multiple
>> instances of the same one).
>>
>
> I don't doubt that this is likely true in general, but I've run multiple
> instances of Exim4, even with separate config files and using different ports
> between the instances (but the same IP address), and that worked fine. Later
> I was able to be more clever and merged it all to a single config file and
> got
> the one listening daemon to listen on multiple ports with a config option --
> and I did that simply because it's cleaner and easier to understand and debug.
>
> If you're wondering how multiple Exim4 daemons could possibly all write to
> the
> same log file, well, the same is true for every Exim4 process that gets
> forked
> off into a thread for each mail transfer.
>
>
>> Take it from someone who's run three of them on the same server. If there's
>> a distro that knows how to handle multiple MTAs, I'd also like to hear about
>> that, so it's a pretty safe bet that you have one, and only one installed.
>>
>
> I've never tried to run multiple *different* MTAs at the same time -- that I
> can imagine being ugly and unpleasant, because there are differences in
> logging between MTAs among other things. And I can see several other
> problems
> with the idea -- the 'mailq' command would have contention for more than one
> MTA, so you'd have to install the 2nd MTA in a different path and specify the
> path to the executables in the init scripts as well as when you want to run
> commands... yeah, I can see that being ugly.
>
I have in the past, run two independent instances of qmail and one of
Postfix on the same machine. This was to use Mailman with the Postfix,
one of the qmails was my primary mail service, and the second qmail
provided a SpamAssassin front end to someone else's mail server
elsewhere. qmail uses multiple instances to run on multiple ports, but
these instances share *everything* so when you _don't_ want them to
share everything, it's more involved. ("involved" when it comes to qmail
means a patch)
Today, I run two independent instances of Postfix on the same machine on
different IP addresses This is because mailing lists have become a
major liability issue. People find it much easier to report a mailing
list they no longer wish to be on as a spam source than to unsubscribe.
And then there's various misguided anti-spam systems out there that get
tripped up on rejected list message and things like that. So I don't
want _any_ mailing lists running on a MTA handling "regular" mail.
Should you want to do this, an excellent guide is here:
http://advosys.ca/papers/email/58-postfix-instance.html
It indeed tends to be a problem when you run multiple different MTA
programs, but a little dpkg-divert magic kept it all sorted out through
upgrades.
- Ron
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