The largest ""CON"" for Thunderbird v2 is the poor spell checker, at least for English. It's algorithm for suggestions is very very poor. For example, it's suggestion list to replace ""Imedeately"", a simple misspelling of ""Immediately"", is (in this order): Inanimately, Animately, Temperately, Corporately, Regenerately, Philately's, Philately, Insensately, Sensately, and Intemperately. It never suggests anything close to the correct choice, ""Immediately"". This is such a common algorithm failure that the spell checked is of little use.

I know a few people using Thunderbird for PC and say it works great. So PC users may have better luck. I've been using Thunderbird for MAC for 2 months and need something better -- CONS: • slow -opening, downloading, & viewing Emails -AND SENDING!!! • Sorting - sorting emails by date....y bother trying? Emails don't get sorted properly. Recommend sticking w/MAC mail supplied w/your MAC, or finding another one....

While this is an otherwise amazing program, it has a longstanding major bug that makes it absolutely unusable if you need to receive regular large attachments. The program will often take enormous amounts of time to download when compared to other clients, and requires that file to re-download every single time that message is opened. When this is eventually fixed it will be the perfect client, but this bug goes beyond annoying to debilitating.

The reviewer who couldn't change fonts or insert a signature simply doesn't know how to use the program. To use HTML formatting (which allows use of any of your installed fonts at any size) Check Tools -> Account Settings -> Composition & Addressing -> Compose messages in HTML format for each account if it isn't already checked. Easy! HTML formatting will work for just about any email recipient and is the default setting. Firefox is super stable, too. Something else is causing your crashes. Better fix it. The first 2 reviewers are not knowledgeable. Firefox is the best email client available, and not just because it's free, stable, and secure.

Won't let you set your own font choices or size. Don't even try to set up a signature. Worst program of any type I've used. Not user friendly at all. Stay away.

I've used Thunderbird successfully for months, until the latest automatic update in November 2008. Thunderbird now fails to really close when it's closed, and it crashes my Intrnet connection. I have to reboot many times a day. The problem with this type of software is that there's no one to complain to! The hoops I'd have to jump through to file a Bugzilla report are more work than just ditching this software and installing something stable. There's no one who can troubleshoot or let me know if there's a workaround. Very frustrating, wish I'd never installed this hunk o' junk.