It could be the following: Most AV programs that provide scanning of outgoing messages work by appearing to the e-mail program as though they are the e-mail server. So, OE sends the e-mail, which is intercepted by the AV program and this doesn't take long. The AV prog scans the attachment and then starts sending it to the REAL e-mail server. This takes longer. If you have OE set to "Hang up when done", OE disconnects before the AV program has finished sending. The simple answer is to ensure that OE is not set to hang up, and don't close OE until you know that all e-mails have been sent (I don't know about McAfee, but most AV progs have a system tray icon that tells you the status of the outgoing stuff)