How do I stop mail.app and its nag screen from opening upon login in OS X if I don't use it

"This is probably related to iCal.

I have the same problem and I use iCal in sync with my Google calendar, which is configured to send emails for certain events.

Disabling Automatically receive invitations from mail in iCal preferences does not help.

This post has some more info:

discussions.apple.com/thread/1853470"

"I'm experiencing the exact same behavior on 2 of my systems (10.6.2 & 10.5.8)

I think the behavior may be connected to ical
Do you use it?

On my leopard system I have never used mail and mainly run it remotely as a server, however I used ical to mirror the my Google calendar from my main system. The message I get from mail on the setup screen has details of my Gmail etc, presumably from ical as I haven't entered this info on mail ever.

On my main system I also get the Gmail detail prefilled. I had assumed this was because I used to use mail and have since went back to Gmail and it had lingering details of previous accounts, however no believe it is linked to ical (which I still use)

Try going to ical preferences (if you use it) going to the advanced tab and disabling 'Automatically receive invitations from mail'

I have just tried this myself and will let you know if this works. Perhaps ical is polling mail for some Gmail info (as the account is shared between Google calendar and Gmail) and is consequently trying to create that account.

Anyway just a thought, it would be interesting if you have a similar ical/Gmail integration."