Sending Multiple Copies Files w/Large Attachments

I am an instructor/consultant. I have several clients with the following problem(OL2003 and 2007), and twice experienced it myself:
I send an email to 1 or 2 persons with large attachment(s) (2-7MB).

It takes forever to clear the Outbox, generating messages like "waiting for server." It continues to send, and it may not clear at all, in which case it is sending another copy every 2 minutes! The recipient reports receiving many copies, most of which have corrupted attachments--in one case the files totaled 4MB and over 90 of them were rec'd, every 2-3 minutes, before they called and I cleared the item from my Outbox.

My ISP is Verizon DSL, another is a local Tellurian DSL. All times of day, morning, afternoon, 3am (yesterday).

Someone commented that the "send is timing out ", whatever that means. The fact that it is getting stuck in the Outbox would seem to indicate to look for an OL solution.

 

The Verizon account is not the issue, nor the Tellurian account--both accommodate up to 20 MB attachments using OL.

I found a lot of similar threads on many sites, so this must be prevalent. Most users attribute it to malware, but we have ruled that out pretty thoroughly.

I looked around the KB without success, then someone pointed me to KB813514, which obscurely references changing the time out for the server. No mention if that will work, mind you, or even work for OL2007. When I have to send the next big file, I can test it. If the server time-out change works, someone should be making that solution common knowledge.