I have another find: I tried to set up a gmail account following the google instructions on a guest account on the Macbook. For once, everything seemed to work and the account went online, even found some emails....too many in fact! it looks as if it's trying to download 2281 messages!!!! All the content of my online gmail a/c it seems....

I had the same problem after using migration assitant (along with a bunch of other glitches) and decided that I would delete the plist file to see if that solved anything. Low and behold it worked. I deleted my accounts first, but I don't think its necessary. The plist file is located under your user folder at /library/preferences/com.apple.mail.plist. Hope that helps.