Thunderbird is, and long has been, the first choice PC email client of every technical magazine that I've ever read. It's also widely recommended in the general consumer press, on BBC technology programs and across countless websites. Add to that it's undoubted popularity among ABers, and I reckon that you should be fairly safe to use it ;-)
(Thunderbird is 'out of the same stable' as Firefox, even though it's now developed by separate teams, and should thus be regarded as excellent).