Protecting Your Small Domain from Spam Hijacking?

Black Cardinal asks: "I have a small domain which I mostly use to post family photos and some software. I also use it to manage a few e-mail addresses that my wife and I use. A spammer recently hijacked my domain name, using it to construct fake return addresses for sending spam (without actually cracking my host account), and caused a flood of undeliverable mail messages to be sent to my domain hosting service, which promptly suspended my account. At the moment it looks like I may never be able to have any @gelhaus.net e-mail again. What can I and my domain hosting service do now to protect their incoming mail servers and my account from this kind of attack, and how can I protect my small domain from this kind of hijacking and allow me to keep it running?"

"My domain hosting service, CubeSoft, has been a good host for my domain for the past three years, and they have been very helpful in re-enabling most of my account, but at the moment they don't want to re-enable my e-mail because of the flood of returned spam coming in (30,000 messages per day). Since the return addresses are all invalid (e.g. 'nonexistent_address@gelhaus.net'), I would think it would be simple to filter out all messages that aren't specific ones I've set up (e.g. 'valid_address@gelhaus.net'). I can't believe my domain is the first to have experienced this problem. It would be a tragedy to have to just shut down my domain because of this. CubeSoft says there isn't any way to prevent it because there is nothing that stops a spammer from using a fake return e-mail address. What have others with small domains done to protect themselves?"

Comments

Just wait it out

[Lord Grey]

Your problem may be due to the worms working their way around the Internet rather than due to a spammer intentionally using your domain. My email server recently suffered the same fate (though not quite that high of a volume) and I spent a bit of time tracking down the emails' origins through the bounces. In my case, they turned out to be coming from just a few unique systems and the volume slowly trickled to nothing after several days -- presumably because someone finally got around to patching their systems.

All the above is conjecture, of course. But it may be something for your ISP to think about. It may be possible to re-enable the MX for your domain in a short while without having to do anything.

One small thing that you can do

[martinde]

We have had the same issue, unfortunately. I asked on the debian-isp mailing list about it and the only real suggestion was to report the spammer in question to their ISP, which I believe to be in Russia.

The long and short of it is that we couldn't do much about it, other than try to minimize the resource waste. In our exim configuration we turned on "receiver_verify" in our exim configuration, which means before the incoming message enters the delivery phase, it's verified that there is a valid receiver. (Before doing this, the incoming message would run through spamassassin and then generate a bounce, using CPU time, memory, etc.) I know it's not much; I hope someone comes up with more suggestions.

Re:As long as email isn't replaced...

[anthony_dipierro]

But nobody seems interested in a modern-day email alternative.

Just about everyone is interested in a modern-day email alternative. The problem is getting everyone to agree on which particular one to use.

Not much you can do at all

[BrynM]

CubeSoft says there isn't any way to prevent it because there is nothing that stops a spammer from using a fake return e-mail address.

Unfortunately, they are 100% correct. The spammer is just using your server as a destination for MX record lookups. When a spam is sent, most receiving e-mail servers will try to do a reverse lookup on the "from" or "recip" address via a DNS lookup or an MX lookup. This prevents the spammer from just blanketing a server with a completely made up "from" addresses (which used to be a popular tactic). The spammer now has to have a legit domain, so he used yours and just made up the account portion.

So, what happens when the receiving e-mail server tries to verify account name too? The spammer has to use someone's real account name (which has happened to me more than once). Since the spammer is using his own mail server to send the messages, your account and domain names don't only get checked ageanst your mail server when the recipient server tries to verify that they exist and not when the spam is originally sent. Thus, it's almost impossible to prevent.

Your only hope is finding the spammer somehow and making them miserable in some way (getting their ISP to cut them off, legal action), but that usually leads to the spammers friends making an exaple out of you (yet more unfortunate personal experience). I would just wait it out. Your ISP is doing the only thing they can by disabling your domain's e-mail. Soon, the "from" lookups will start failing for the spammer and he/she'll have to pick someone else to impersonate. I hope that your ISP will let you re-enable your domain's e-mail when it blows over. Good luck!

Re:You're smart...

[Just Some Guy]

Exactly. I went through this about two months ago. I was getting about 2,000 bounce mails per hour until I added a bunch of lines to my Sendmail's "access" file, recompiled access.db, and restarted sendmail. Here's an example entry:

erin@honeypot.net "550 This account was spoofed by some jackass spammer. It doesn't exist and never has."

Add one for each falsified account. You will still get the incoming SMTP connections, but your server will reject the mail before the sending host transmits the whole thing. Advantage: you lose the bandwidth that it takes to build a TCP connection and send a single RCPT line, rather than losing the bandwidth and storage required to process and bounce a whole message.

My SMTP bandwidth graphs dropped about 85% after adding those filters. Do the same on your end (or have your ISP do it for you) and sit back while the storm blows over.

Oh, yeah: you may want to put a prominent notice on your website's main entry point stating that you are not the originator of the spams. The flood of mail to my "abuse@" address tapered off greatly once I explained things to visitors. I still get a few twits with an axe to grind but there's not much you can do about that.

Thanks for the replies

[Black Cardinal]

Thanks to everyone who's posted replies on my topic. I've worked with my hoster to change my default alias to route messages with an invalid address to oblivion. Until this happened I didn't even realize that I had a default alias set up, which shows how dangerous a little ignorance can be. We're now re-enabling my aliases one at a time and watching closely to make sure these valid addresses are not being overrun with this returned spam.

By the way, I should mention that my hosting service, CubeSoft, has been very good through all this. I've been in constant contact with them through e-mail (but not my domain e-mail, hah), and they have been very helpful in suggesting solutions and in trying to work with me rather than just blowing me off as not their problem. After this, I can strongly recommend them as a hosting provider.