To handle real incoming mail for real business customers who aren't interested in Nigerian wire transfers and male enhancement,
Google Apps. It's only $5/mo/user, and provides more than just e-mail.
To handle real outgoing automated mail, services like
Mandrill for transactional mail and
Mailchimp for bulk mail are excellent.
Yes, these services cost money. Turns out that
setting up an e-mail server is trivial, but becoming trusted to send good mail to the rest of the world is not easy.
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