I use ASPMail as well. What I've done is made a table in a MS SQL Server DB as a message queue. When I want to send an email automatically, I add a new record to the message queue. Then I wrote some
VB in an ActiveX Script in a DTS object that queries the DB for new records in the message queue, flags the message sent, attempts to send the email using the ASP COM object (if it fails, I change the flag back to unsent), repeat through the recordset of unsent records. Then just schedule the DTS package to run every 30 minutes or so.