If I were you, I would create separate signatures for each account. In Outlook's Options->Mail Format tab, set each account to use the designated signature. When you use the POP3 account signature, it should force the mail to go out on the POP3 account.
Of course, all replies will use the receiving account and will have to be changed manually if you want a different account to reply.
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Milly Staples [MVP - Outlook]
Post all replies to the group to keep the discussion intact. All unsolicited mail sent to my personal account will be deleted without reading.
| Outlook 2007 always changes the default "send from" account
| from my POP acct to the exchange acct. I can reset it, it gets
| set right back. Any thoughts?