SA-Exim: bye bye spam — 2 years ago
Three months ago I ended the contract with my hosting provider (they really pissed me off), so I decided to put a server in my appartement. I took a while before I was able to buy a new desktop , because I was waiting for my Ph.D. grant to arrive. But it was worth the shot: since then I don’t have spam anymore.
I use exim4 as the mail server with the SA-Exim plugin and since sa-exim works at MTA level, spammers cannot tell if their spam was filtered or the mailbox doesn’t exist, so the address is progressively deleted from the spam lists (well, actually they could know, since “User uknown” is rejected after the RCPT command, while the spam is rejected after DATA. Hopefully not all spambots are so smart: some of them are even so dumb as to send commands before the server has time to answer and this fact is a breach of SMTP protocol and implies the shutdown of the connection).
Another hack I can use now (and I couldn’t with my previous ISP) is to use unique e-mail addresses . Obviously a spammer can steal a user+unique_id@example.org address and try to send spam to user@example.org. The countermeasure to this behaviour would be to invalidate all user@example.org addresses and accept mail only for user+unique_id@example.org (and put the list of acceptable unique_id into users home directories).
