Depending on how you send e-mail, your current IP (at that time) might be present in the Received:
header of mails other people got from you.
Try and send an e-mail to yourself and look at its source code (how to do that depends on how you access your mail) and compare the addresses that show up in the various Received:
headers to see whether your current address appears there.
If it does, you “just” have to somehow get one of the e-mails you sent at the time you’re interested in. You might have sent one to a friend or to a mailing list.
(Yes, the chances to find the IP this way are pretty low, but depending on how important it is to find it out it might be worth the effort.)
I will check the log files, that is a good place to start. Thanks! – Taptronic – 2010-08-12T15:24:12.657
Good start but the log file doesnt go back but 5 days on my router. :-( Any other log somewhere else on the PC maybe? – Taptronic – 2010-08-12T15:31:28.673
2Maybe there are some webpages that you use frequently that track your IP? Gmail tracks IP, but only for the past 24 hours. – Jarvin – 2010-08-12T15:37:06.690
@Optimal Your PC doesn't register your external IP addresses... if it's not in your modem, you probably wont find another log that goes back 6 months. – BloodPhilia – 2010-08-12T15:38:08.127
Thanks - was afraid of that, but hopeful though! :-) – Taptronic – 2010-08-12T15:42:01.253
1If you were to call your ISP they should have records but the odds of them actually providing it to you are slim-to-none. – Shinrai – 2010-08-12T16:01:18.760