Squirrelmail on Web Server?
 

I normally have SM (webmail) on the same physical server as my Postfix mail server. I realized that it would be much more simplistic for me to avoid installing / configuring Apache on my Postfix server and just use my web server on the same LAN. Can I install Squirrelmail on my web server and have it connect to my Postfix server?

web_srv = 192.168.0.100/24
mail_srv = 192.168.0.101/24

yes absolutely, you'd just specify the smtp and (presumably) imap servers within in the config file explicitly. http://squirrelmail.org/docs/admin/admin-5.html

So before I would have SM on my mail server with Apache installed:

https://mail.mydomain.com/webmail

But now I would like to add this to my web server, I would assume I would simply change it under the document root as:

http://www.mydomain.com/webmail

Is that right?

yeah, i've not used squirelmail for a while, as I think it's a steaming sack of arse compared to just about anything else, esp horde/imp or roundcube, but it's very simple to graft it on wherever you want in an app. Personally i'd pick a new fqdn, e.g. webmail.domain.com, running on the same web server, but that's just a style / preference thing.

Do you prefer roundcube or horde over the other? I really like the alternatives!!! SM seems so dated and blah.

when horde/impp works, it's quite nice. Maybe a little dated now, but still very professional looking, unlike SM. In general open source webmail is a suprisingly weak area, roundcube is pretty new and coming along well though.