Tonnes? I don't like to say 'just search for it', but seriously you'll get more out of that than a response here. Personally I use SES for the 'hard' bit, but there's loads of OSS if you want to self-host the actual receiving too. (Sending probably requires more time looking into getting a trustworthy static IP than software. Again, I bypass that by using SES, but that's technically only self-hosting storage & client.)
