I manage IT for a large organization with over 2000 people. The administration would like to send an email (often with up to 5 word document attachments) about once per week.

They also want to categorize people. For instance, about 40 people are "teachers," about 1800 people are "students," and about 10 people are "board members." They may send an email to any combination of these categories.

Here's what I have tried: I bought a server, installed Ubuntu server edition on it, and wrote a python script to send out their emails. However, pretty soon, mail services such as Gmail and Yahoo began to treat the mail I send out as SPAM. I'm guessing this is because I am sending an email with 2000+ people in the "bcc" field. Maintaining this server also takes a lot of time.

How do I set up a mailing list for over 2000 people? Must I defer to paid services?