Are you using .Mac email. Are you missing any emails? Are you sure? How do you know?Well a growing number of people are complaining to Apple that they are, and they only found out because someone complained about not responding to a previous email. The missing emails were at first thought to be a problem with .Mac and Gmail senders, but as the posts grew, it has become apparent that the issue spans many well known corporate domains.
So far Apple customer service reps have no fix for the problem, and some callers are being denied tier 2 support and being told its an intermittent issue. The posts started on June 6th, but the issue seems to have started before that date for some. Some have even said they were told that the missing emails would be in their webmail, and only desktop .mac was effected. This too is posted to be inaccurate. Even others have been told that the missing emails are probably gone for good, lost the the web abyss.
Have you been affected? Many have run their own tests, sending bulk numbered emails to their .mac accounts from other email accounts. Many have reported not receiving them all. Missing 1,2 or 3 out of 10. Are you effected? I suggest you run your own tests and see. If you are, you can find more details here: Apple Discussions Forum - Missing .Mac Mail Thread
Looks like they havent worked out all the .mobileme bugs yet. If you are missing email, you may want to report the problem to Apple Care at 1-800-275-2273.