Mail Scheduler for Mac

From Mountain Rose Multi Media:

Mail Scheduler is the ultimate utility to send delayed and repeated messages.

There are several ways to use Mail Scheduler, while it's still pretty easy to use.

A couple of the major features are:

• Send simple messages by entering the subject, email addresses en text.
• Use your standard email application to create complex messages. Even html messages and attachments.
• Send messages once. Want to send a message two years from now? No problem! Just add it to Mail Scheduler, set the date and forget about it.
• Send messages every year, every month, every day or even every hour.
• Progressive schedule: Send a message each xx days and slowly decrease the interval time down to every hour. This is the perfect way to make sure you'll get an answer!
• Has its own SMTP Server and HTTP Server, so you can run it either on your own or on another computer.
• Use your browser to adjust the schedule of any message.
• Runs in the background.