I wasn't sure whether what I'd said was true, so I've tracked it down again. (I did once research this, and was going on memory.)

An overview of different time systems is at
http://sadira.gb.nrao.edu/~rfisher/Ephemerides/times.html

More detail is at
http://www.faqs.org/faqs/astronomy/faq/part3/

Neither of those answers the question of timezone notation. But ISO 8601 does, and that can be found explained at
http://www.cl.cam.ac.uk/~mgk25/iso-time.html

I'm posting this at 2001-08-24 12:12Z and my local time is 12:12 + 01:00 (meaning 1.12 p.m.) because we're on British Summer Time here. The Z does stand for "zero meridian", i.e. Universal Time (formerly called Greenwich Mean Time).

But yes, e-mails arrived postmarked at your local time (if you can get the jolly thing to work) so they use a notation effectively the reverse of that for local convenience.