How do I prevent Outlook from changing the outgoing email account

[Richard de Oldphart]

When my default email account with one ISP is not available for some reason,
outlook decides to send the email out via one of my other accounts with
different ISPs without any notice to me. This causes the message to come from
a different account. Some of my recipients have mail filters that only allow
recognized senders and my message ends up in the junk file. This has created
some big problems.

I cannot find a setting that either permits this or prevents this action.
How can I stop this from happening?

This is with Outlook2003, SP1. (I never experienced this with earlier
versions.)

Thanks.

 

[Brian Tillman]

When my default email account with one ISP is not available for some
reason, outlook decides to send the email out via one of my other
accounts with different ISPs without any notice to me.

The word is that Microsoft's next service pack for Outlook will change this
behavior to produce an error instead of simply choosing another account.