JayFCatskills, this is not a error from Avast. It has to do with your ISP's mail server most likely. Basicly what happens is this:
1] You create a mail.
2] You click on send.
3] The mail server of your ISP receives this info.
4] OE is starting to send the mail after receiving a "ok" from the mail server
5] OE starts sending.
6] Avast notice this (if you have set 'scan outgoing mail) and starts scanning
7] The mail server is waiting.
8] The mail server does not get a response within a (defined time by your ISP) time.
9] The server thinks something is wrong and gives the time-out error.
One solution is to disable the outgoing-mail scanning. While Avast is scanning the mail, the server is waiting for a response. The larger the mail is, the more time it takes for Avast to scan it. Very logical. But the mail server is inpatient

and doesn't want to wait that " long". So it generates a error.