Drupal Association members fund grants that make connections all over the world.
The reminder watchdog entry is always inserted, even when the message has not actually been sent due to an error or a message alteration (see #800434: drupal_mail, allow hook_mail_alter implementation to cancel mail).
Testing the message result should be enough. Attached also a backported patch to 6.x.
The patch in #1 applies fine and fixes the issue.
Committed to D7, thanks!
Drupal is a registered trademark of Dries Buytaert.