When sending group emails, I place the designated group into the BCC file, (avoid sharing email details) when I check the sent file, I find it only forwarded the email to 16 of 53 address's. The next one sent to 21 of 45 address's. The next one sent to 26 of 58 address's.  I have tried redeveloping the groups to be smaller and it does not make any difference.  Sometimes it will send to the entire group of 53, or whatever the quantity is.  I have done the update provided by LenMaggiore, it worked for one send, then dropped address's in the next email.  I do all updates from MS, and still cannot get consistent sending of emails?

What else can be done to fix this? I await your solution!