More information can be found on the web, including the on the web.
Reappearing Mail Messages
Make sure a checkmark appears in the box next to Delete retrieved mail on
host.
Pegasus can be configured to read mail offline, or without being connected
via modem. In order to do so, these changes must be made:
Reading mail offline
Trumpet Winsock must be reconfigured so it does not try to autodial when started. To do so, start Trumpet and press ESC twice. This will abort the script. Press ALT-D. This will pull down the Dialing menu. Select Options..., or press "o".
Minimize Trumpet and start Pegasus.
Press ALT-F. Select Network Configuration.
Set Poll new mail after to 0. Remove the checkmark from Check when opening new mail and Send mail at once (don't queue). Press OK
Press ALT-F. Select Preferences.... Select General Settings.
For more information, check the Pegasus Home Page.