Some clarifications about Messages.app in Mountain Lion After the update to Mountain Lion I see that I have four accounts in my Messages app (see this question for more information). I am a bit confused about what happened here, namely:


The @mac.com account has always been used for iChat, but now in
the Messages app it looks like it is used for iMessage
My Gmail account was used on my iPhone and iPad (I say "was" because
I haven't used iMessage on my mobile devices for a while), but now
it looks like it is used for GTalk in the Messages app
I have never used Bonjour for message exchange, why does it appear
now in the list of accounts?


Why have there been such changes? If I leave the situation as it is now, does it mean that I cannot receive iMessages on my Gmail account but only on the @mac.com account?
There are several things going on here. First, and easiest, Bonjour just appears as an option that you can configure if you have a Bonjour account. No need to worry about that.

As for iMessage, you can have more then one email address that other iMessage users can message you at. For example, when I open Messages settings I have a few different accounts in there. Bonjour is disabled, and two Google Talk accounts which I have disabled also. When I click on my "iMessage" account, my iPhone number as well as several email accounts which are linked to my Apple ID show in there. So I have my Gmail (which I use for my Apple ID), my @iCloud.com and @me.com email accounts, as well as two others that I have arbitrarily added in so that other users can text those emails as well.

Messages.app on Mountain Lion can manage multiple types of instant message at one time. For example, I can have a Jabber account, Google Talk account, and my iMessage account all tied into Messages. When someone "pings" any of those accounts, Messages "handles" that and I can reply.