You may see an error in your SendMailLog.txt similar to:
2010/07/12 14:53:22 Q 10 messages. 10 are bad.
2010/07/12 14:53:30 LOG <AB64>67#
2010/07/12 14:53:30 NEW Q: C:\Program Files\CatTools3\MailQueue\rad436D7.eml
2010/07/12 14:53:30 LOG Mail queue has 11 entries
2010/07/12 14:53:52 Q 11 messages. 10 are bad.
2010/07/12 14:53:52 LOG Mail queue has 11 entries
2010/07/12 14:54:22 Q 11 messages. 11 are bad.
2010/07/12 14:56:52 Q 11 messages. 11 are bad.
2010/07/12 14:57:20 LOG StopQMonitoring invoked: 0/11 good messages still in queue
2010/07/12 14:57:20 Q Off
2010/07/12 14:57:22 Q 11 messages. 11 are bad.
2010/07/12 14:57:30 LOG Mail queue has 11 entries
2010/07/12 14:57:52 Q 11 messages. 11 are bad.
2010/07/12 14:59:22 Q 11 messages. 11 are bad.
If you get this error, check you check your E-mail addresses in the Send To section of the General Options tab of your E-mail settings. Make sure there is no “,” after the last E-mail. If there is the comma, delete it and click OK.