smtp

ActionMailer::Base.server_settings = {:address => "smtp.gmail.com",:port => "587",:domain => "localhost.localdomain",:authentication => :plain,:user_name => "someusername",:password => "somepassword"}

Quoted: How to configure DNS for correct validation of email services.

Quoted: What is SPF? SPF fights return-path address forgery and makes it easier to identify spoofs. Domain owners identify sending mail servers in DNS. SMTP receivers verify the envelope sender address against this information, and can distinguish authentic messages from forgeries before any message data is transmitted.

Quoted: To ensure that Gmail can identify you:
* Use a consistent IP address to send bulk mail.
* Keep valid reverse DNS records for the IP address(es) from which you send mail, pointing to your domain.
* Use the same address in the 'From:' header on every bulk mail you send.
We also recommend publishing an SPF record, and signing with DomainKeys.

Quoted: XMail is an Internet and intranet mail server featuring an ESMTP server, POP3 server, finger server, TLS support for SMTP and POP3 (both server and client side), multiple domains, no need for users to have a real system account, SMTP relay checking, DNS based maps check, custom (IP based and address based) spam protection, SMTP authentication (PLAIN LOGIN CRAM-MD5 POP3-before-SMTP and custom), a POP3 account syncronizer with external POP3 accounts, account aliases, domain aliases, custom mail processing, direct mail files delivery, custom mail filters, mailing lists, remote administration, custom mail exchangers, logging, and multi-platform code. XMail sources compile under GNU/Linux, FreeBSD, OpenBSD, NetBSD, OSX, Solaris and NT/2K/XP. Read the file README.TXT included with the distribution.

This works, and it's zero config.

Quoted: Free SMTP Server supports all email programs