Recently set up BIS (had used BES - no longer available). Carrier is T-Mobile. Email is Comcast but using Outlook, not Comcast webmail. Don't understand why not all emails going to Blackberry. Seems that if delivered to Outlook when BB email not running, will not go to BB. However, that is not always the case (i.e., sometimes leave Outlook running and emails delivered to both Outlook and BB). In Outlook, emails are delivered to online folder - I don't have a rule to move to offline folder.

Any help understanding what is going on?

This will probably help: Some email comes to my BB and some does not - BlackBerryFAQ.com

Do you have "Leave mail on server" checked in the Outlook setup, under Advanced Options?

Thank you both! I had read that first suggestion but hadn't found where in the Outlook set up that was (I thought it may be something new with a later version of Outlook (I'm running 2003). I have now checked that setting and hopefully it works fine now. The suggestion sure makes sense!