I have a site where people enter their email address to be reminded of a weekly posting. I only send them the weekly email that they double-opt-in for. I do not sell, trade, expose, or do anything else with their address.

Right now I have a bit of a hack, connecting to a large email providers SMTP server to send the emails. As the site grows I fear that my emails will be marked as spam and that I will be violating the TOS of the provider.

I'm considering two options, building an in-house SMTP server or using a mailing list service. Is there a best-known-method for this?

I'd really prefer to simply build my email and use a script to send them through the SMTP server rather then use some GUI to build the email and import a list of addresses. But previous experience tells me that running a mail server and not being marked as spam can be difficult.

Help!?