Proper Ways to Dispose of Spam? 119
An anonymous reader asks: "My domain name is being stolen by spammers; they forge outgoing mail using my poor innocent domain name. First, I'd like to plead with mail server administrators out there: please REJECT spam and undeliverable mail. If you reject instead of bouncing then legitimate mail senders will still know there is a problem. Second, do you have any tips for dealing with a flood of spam bounces? Exim is pitching the bounces pretty quickly, but my server is still getting overwhelmed."
In the case of stolen sender addresses, SPF attempts to address this problem but has it been effective?
Backup MX is to blame for some of this bouncing (Score:5, Interesting)
Are you running your own backup MX? Probably not. It's often a generic spooler your ISP lets you use for convenience. Even if you do, does your backup MX have all your rules in place, so it knows what to reject? No, I bet not. So this backup server accepts the mail without question, then passes it to the primary, and then it gets bounced.
We need to either have a way to give our backup MX our rulesets (which the people who run the backup servers understandably won't like), allow backup and primaries to just silently discard (which legitimate senders and receivers won't like), or, quite possibly, stop using backup MX entirely, and then if the primary goes down, the originating mail servers should do their normal pattern of retrying for 5 days, or whatever.
Large companies who need 100% instant availability of mail shouldn't be using backup MX anyway, (I've seen backup MX servers configured to hand off to primary hourly or even daily, not to mention those that hold until the primary asks for the mail) they should be using a ring of servers sharing primary preference. I'd expect the ruleset to be identical across the ring, thus allowing for instant rejection all the time.
SPF hasn't helped me much (Score:2, Interesting)
- Don't use catch-all addresses. Normally blowback is not addressed to a valid user. This was not an option for me, but it may be for you.
- Reject invalid bounce messages. Any message coming with an empty envelope sender to an address that has never sent mail on my system is considered invalid and rejected during SMTP with a message stating why. This is what I chose.
The reason for my choice is that it consumes minimal resources (all that's required to reject a message is one SQL query against a small, in-memory table), informs the bouncer of the problem, and eliminates 99.99% of blowback (some incorrectly-configured MTAs produce bounce messages that don't have empty envelope senders... I get like one of those per month).And I second your pleading: Please, please, please, mail admins, please reject email during SMTP instead of producing bounce messages! Please!
Re:anyone have a domain where this DIDN'T happen? (Score:5, Interesting)
I got a call from a sysadmin somewhere in nowheresville USA. The minute I picked up the phone, the guy started berating me, since I was destroying his domain, and it was all my fault, because I'm running Exchange and obviously I was infecting him with Winblows.
After I finally got things sorted out, I walked him through exactly how and why it wasn't our domain a'tall, which would have been obvious had he looked at the headers of any one of the thousands of emails he claimed he recieved. If he knows how to read any of them. When he realized he was wrong, he slammed the phone down midsentence.
Point of the story: SPF is great, proper mail server administration is great, but there will always be jerks who think they know what they're doing when they don't, and they're the bane of the whole system, more like a wolf in sheep's clothing than a known enemy.