Mailing lists in rails?

It is possible, but slow. For every mail, ActiveMailer re-establishes the connection to the SMTP server (and this sometimes fails under load)

I made some changes to the ActiveMailer code to open a connection and then send the email, passing in the connection. I don't have that code anymore, but it wasn't hard to write once I knew what I needed to do.

20-30K messages is about where I'd start thinking about doing something different. Below that, you should be Ok with ActiveMailer.

The main problem I had was not Rails related, but Spam related. I had so many bounces due to various conditions - old email addresses, spam filters etc. You will get into trouble if you do this a lot and don't process the bounce messages to disable email accounts for future mailings.

Bounce messages come in many forms - one email server actually has some comments from the programmer essentially saying: "The standard for bounce messages is too complex, so I'll invent my own format that's easier". You have to handle this format as well as the standard formats, so it turns out to only be easier for that programmer. Can you tell I'm still grumpy?