My Outlook program used to work perfectly. Yesterday, I tried to e-mail a 1
MB video file (about 30 seconds of video w/ sound), first as a regular e-mail
attachment and then after saving it and attaching the file via Windows Movie
Maker.
Since then, I get the following message over and over again and my outgoing
messages sit forever in my outbox:

'Task mail.comcast.net-Sending and Receiving' reported error (0x800C8105):
'Unknown Error 0x800C8105'

The send/receive progress window also says 0 of 29 [or more] tasks have
successfully completed.

Can anyone help me pls.? Comcast, my ISP, says its not their error. (An
aside: Why doesn't Microsoft provide any support itself?)