One of the great things about Google Apps for Domains is they run a mail server for you, and you get the GMail web interface for email. Not only that, but you get a fully functional IMAP server as well.
Unfortunately, GMail has a few annoyances.
GPG
The first annoyance is the lack of support for GPG. Fortunately this is easily overcome with the use of FireGPG extension for FireFox. FireGPG provides a simple easy interface for using GPG, including, but not limited to, digitally signing emails, encrypting email and attachments, and GPGAuth.
If your not into GMail, FireGPG can also support Rouncube Webmail. It also provides an easy mechanism to import GPG Keys, you know those big hash like things people paste on their sites; with one click you can import them.
Fixed-Width Fonts
The other major annoyance, which I find extremely annoying, is GMail displays all emails in a variable-width font instead of fixed-width. There is a "labs" feature that gives a toggle switch to change to fixed-width font, but you cannot make it the default. Fortuantely, again, FireFox comes to the rescue, with it's "user defined style sheets". With only a couple of lines of CSS you can haz your email in fixed-width fonts.
User style sheets are located your FireFox profile directory, and is named userContent.css. Any CSS you put in the file will be applied to each and every site you visit, so we can use it to get back our fonts. In Ubuntu it's located at "~/.mozilla/firefox/xxx.default/chrome/userContent.css".
Just add the following to that file:
/* GMail fixed-width font: see http://3cx.org/item/34 */
div.msg div.mb, div.ArwC7c {
font-family: monospace !important;
font-size: 12px !important;
}
div.yxEQwb {
display: none;
}
div.ckChnd textarea, textarea.tb {
font-family: monospace !important;
font-size: 12px !important;
}
td.ct {
font-family: monospace !important;
font-size: 12px !important;
}
This will give you fixed-width fonts for all plain text emails, in the old and new, GMail interface, and it will hide those annoying "Sponsored Links". Also, it will give you fixed-width fonts on Google Groups. Awesomeness!
Customizing GMail With Labs
In the GMail Labs section there are a bunch of goodies to be had. My favorites are Tasks, Advanced IMAP Control, and Navbar drag and drop.
Tasks are very simple. It gives you a little pop-out at the bottom for which you can add tasks, mark them as completed, link them to corresponding emails, etc. Lovely little TODO list keeper.
Advanced IMAP Controls gives you the ability to Choose which labels show up in IMAP, turn off message auto-expunging, or trash messages when they're deleted from IMAP
. I love being able to choose which label/folders IMAP can use.
Pretty simple, title says it all. You can drag around all the little gadgets to the order of your choosing.
GMail Almost Rocks
As long as you have FireFox, the GMail web interface is almost a complete replacement for those old and clumsy desktop mail apps. Hopefully we'll see some cool new Labs features roll out, like plain text/fixed-width only email 
.
As long as I don't have to maintain a mail server, I'm happy with GMail.
.