We´ve done mailings before using PHP scripts that I´ve written (not spam, just large automatic newsletters) which have been sent out overnight by our own mail server. The problem is that I have to spend an hour or so creating the code for the message.
Since we want to start doing more of these now, I decided to come up with a more automated system so there´s less for me to do (always a bonus). After a days programming we now have a system that does it all! The first stage is a form where we can fill in a subject line and choose the email contact list to send the email to. This generates a mailto link that creates a new message that has the address for the mailing programme filled in along with a custom subject line that identifies the group as well as the subject.
The programme then checks this mailbox every night and if there´s a new message it automatically sends out the message to that group. It also adds code to put an image on the page and sends a copy to another mailbox of ours. The second email account is then checked and if the copy of the message is there, that email is verified as "sent". The image is used to verify the message has been opened. The path to the image on our server has the users email address encoded into it. When the email client requests the image, a php script is run through the old 404 ErrorDocument method and updates the database that that user has read it. It then sends that actual image to the client.
This way the others in the office can do large automated mailings to different groups and track the progress of them without involving me at all.