[Dovecot] How to tell dovecot to use a specific MTA

[Spyros Tsiolis]

Hello again people,

OK. I checked a lot of HOWTOs and documents. One specific document 
describes how one can make dovecot "talk" to postfix.
The procedure is pretty straightforward (taken from the document) :

--
. Configuring Postfix and Dovecot

Turn off sendmail:

service sendmail stop
chkconfig sendmail off

system-switch-mail
(select postfix)
--

This is for CentOS systems.
My question is pretty simple. How exactly does someone tell dovecot
(or the CentOS system) that the MTA used is not a pre-packaged postfix
MTA but (in my case as you have pretty much discovered by now) XMail
compiled from source (no pre-packaged version AFAIK for CentOS; but even
if existed, I would still build it on my own) ?

Any help would be appreciated,

Regards,

spyros