Environment : Win7 Office 2007 SP3
With Outlook 2007 updated till today :
Mail with attachment (xlsm file) sent to existing mail adress is not delivered at the destination and cataloged at the sender site under sent files in outlook (without error message)
The sender is not aware there is a problem !!!
The receiver doesn't see anything (not in junk mail) ==> lost
After long investigation the solution was the length of the attached file name in question
Another solution was to attach 2 files ( a long file name and a short one) ; it worked but don't ask me why
filename was : "Detail inschrijvingen per tasting (V2.1) 21032018.xlsm"
renamed to : "Det insch tasting (V2.1) 21032018.xlsm"