I frequently have to send large group emails to friends and volunteers (I try to keep the groups less than 50 people).  Those emails always get stuck in my outbox and I get no error message from Windows 7 that my email did not go through to intended recipients.  They get stuck in my Outbox and will not go.  Smaller recipient groups (of 2 or 3) seem to go through fine.

Are my groups too large?  What is the magic number?

Thanks.