WordPress MU

I got some complaints about the registration verification mail not coming through to GMail and Hotmail so I checked my logs and both gmail and hotmail said "250 OK", the mail is delivered.

I tried just now and GMail puts the e-mail in the "Spam" folder. It gets through in 30 seconds, but as said, goes to "Spam" and not "Inbox". As for hotmail, I don't know, I don't have - or want - a hotmail mail account.

So the obvious question is: WHY? I don't know why. I know this has been mentioned before, but I'd like to know: Is it because the welcome mail contains some text-string they don't like? Is it because WPMU sends them too many mails about someone making a comment, which makes them think that the big(?) number of mails they get mean it's a spammer? Or WHAT?

Anyone else having trouble with mail getting through to gmail, hotmail and perhaps others?

Keep in mind that the mail setup is good and secure, adn it's been working for ages, I've tested GMail before (months ago) and the welcome mail was put in the inbox, and mail goes through correctly to any other mail provider (well, perhaps not. But I tried a few other (crappy, anyway) services like mail.com and the mail always comes through, do it's anyone's best guess why I'm suddenly on hotmail and gmail's shitlists.

I use Gmail - and a proud user :P - and don't get any troubles with verification emails, or any other mail sent from WPMU. They are all added straight into the Inbox.
Which version are you using, mine is 1.2.1, so something may have changed in the trac, or from previous versions.

I don't know much about gmail, but a decent filtering system will write the reason for the filtering into the mail headers, so check the "spam" mails again, maybe they give you a hint why your email got filtered...

You may want to do a search for the smtp plugin some folks are using around here.

What is the email address the emails are coming from?