You don't, at least not purely using the Outlook Object model.
You can let your users be annoyed by that pop-up and teach them how to use it.
You can drive mass mailings using Word Mail merge.
For one-off messages you can go directly to SMTP yourself using the WSock32.dll... not easy to do and not as rich in features as the Outlook Object model.
Ultimately any solution to this problem is a hack that will be used by hackers and mass mailers (a.k.a. spammers). That's why I say "you don't". If you find a way to do it, somebody will find a way to shut it down.
Randall J Weers
Membership Vice President
Pacific NorthWest Access Developers Group