RE: SMTP relaying policies for Commercial ISP customers...?
Andy, These are exactly my concerns, and exactly what I feel I'm going to hear from the staff and the customers. I am going to go back and make sure there isn't a "better" solution. Thanks for the input. The issue we have as a dynamic IP broadband provider is that it's a royal pain to shutdown a user - especially in regards to just mail. Lets say we have a spammer and a script detects it. We then have to track him back to the MAC address of the modem, lookup that MAC in the customer DB, shutdown his access and then reset the modem. And at the end, he loses all access, not just mail. With AUTH we can just stop mail access. Yeah, sure we could try to push some access list to the modem itself, blocking mail, but those modems are so flaky to start, it'll never work reliably. Can't just block the IP on the mail server because the user will or could just get a new IP, and then you are blocking a legit user. I'm still not sure if the norm is for providers to let t1+ customers relay. I have multiple OC3's and 12's from AT&T, MCI,... Will they let me relay off their servers without SMTPAUTH? Probably not. As always, comments welcome. -- Daniel Ellis, CTO, PenTeleData (610)826-9293 "The only way to predict the future is to invent it." --Alan Kay
-----Original Message----- From: Andy Dills [mailto:andy@xecu.net] Sent: Friday, February 13, 2004 12:35 PM To: Dan Ellis Cc: nanog@merit.edu Subject: Re: SMTP relaying policies for Commercial ISP customers...?
On Fri, 13 Feb 2004, Dan Ellis wrote:
1) Residential Policy: Enable SMTPAUTH and disallow relaying unless the customer has a valid username/password. If you're not paying for a mailbox, you don't get to relay outbound. This should not break anything except those residential accounts that *should* be commercial anyway.
2) Broadband commercial: This is the difficult one. These are the customers that aren't big enough to rightfully run their own mailserver, but they are big enough to have roaming users on their networks (coffee shops, branch offices, hotels, SOHO....). They expect relaying service for either their mailserver or for all their various PC's. At the same time, they don't have many, if any mailboxes through the ISP. My thought is that they should ONLY be allowed to relay via SMTPAUTH by using a residential mailbox login/pass OR they need to purchase a commercial relay service (expensive because of the openness of it) for their IP space.
3) T1+ : These customers should not be allowed to relay unless they purchase (expensive) relay services for their IP space. Of course, they can always use a residential mailbox, but will have to use SMTPAUTH for it and will be restrained by the same policies residential mailboxes have (low tolerance tarpitting,...).
While the amount of effort you put into this so far is commendable, I really think you're barking up the wrong tree.
At the end of the day, what have you done, besides annoy your customers and increase the load on your support staff?
I don't really see what you're suggesting being anything other than a huge effort, solving the wrong problem.
For any responsible ISP, the problem is the spam coming into your mailservers, not leaving. As long as you quickly castrate the people who do relay spam through you, you're not going to have an egress spam problem.
Since you seem to have countless hours to invest in this problem, you'd be better off writing a log parser to identify WHEN somebody is relaying spam through you, so you can react.
Something else I've seen implemented is rate limiting. Keep track of the number of messages sent by an IP over a variable amount of time and implement thresholds.
I'd love to hear some of the conversations you have with your leased line customers, when you tell them they have to pay for "(expensive) relay services" to send mail through your mail server. How many times will they laugh before hanging up on you? :)
That's like the IRS trying to charge you for the forms...
And I'd also like to see the looks on your technical support staff's faces when you tell them they need to assist your ENTIRE USER BASE in switching to authenticated SMTP :)
And then you have to deal with the customers who have MTAs that don't support authenticated SMTP...and on and on.
Whenever the solution is more expensive than the problem, you need to go back to the drawing board.
Andy
--- Andy Dills Xecunet, Inc. www.xecu.net 301-682-9972 ---
On Fri, 13 Feb 2004, Dan Ellis wrote:
The issue we have as a dynamic IP broadband provider is that it's a royal pain to shutdown a user - especially in regards to just mail. Lets say we have a spammer and a script detects it. We then have to track him back to the MAC address of the modem, lookup that MAC in the customer DB, shutdown his access and then reset the modem. And at the end, he loses all access, not just mail. With AUTH we can just stop mail access. Yeah, sure we could try to push some access list to the modem itself, blocking mail, but those modems are so flaky to start, it'll never work reliably. Can't just block the IP on the mail server because the user will or could just get a new IP, and then you are blocking a legit user.
Yes, that is a little bit stickier of an issue, IFF your goal is to somehow continue to provide the would-be spammer with the ability to send traffic to the net, provided it doesn't transit your mail server. I feel that you're overlooking the simple solution. Blocking the entire account so they can't access anything is the proper response to a spamming incident.
I'm still not sure if the norm is for providers to let t1+ customers relay. I have multiple OC3's and 12's from AT&T, MCI,... Will they let me relay off their servers without SMTPAUTH? Probably not.
I'm almost positive they would. Hell, many providers will give you a free NNTP feed if you want it. The goal is to maximize the use of the link between you and the customer while minimizing the use of the links between you and other networks. Services like SMTP and NNTP are great for that. Andy --- Andy Dills Xecunet, Inc. www.xecu.net 301-682-9972 ---
You wrote: [...]
Yes, that is a little bit stickier of an issue, IFF your goal is to somehow continue to provide the would-be spammer with the ability to send traffic to the net, provided it doesn't transit your mail server. I feel that you're overlooking the simple solution. Blocking the entire account so they can't access anything is the proper response to a spamming incident.
If you block the entire account then the user can't use the account to download the updates your Abuse Team will responsibly want to point him/her at. If you want to lose the customer then that's your business. If you want to keep the customer, helping them fix their mistakes is probably a painful and thankless task - but important and useful to the whole Internet community. Regards, -- leo vegoda RIPE NCC Registration Services Manager
Leo Vegoda wrote:
If you block the entire account then the user can't use the account to download the updates your Abuse Team will responsibly want to point him/her at. If you want to lose the customer then that's your business. If you want to keep the customer, helping them fix their mistakes is probably a painful and thankless task - but important and useful to the whole Internet community.
It is probably worth mentioning that numerous malware today make an effort to block an user from accessing AV or windowsupdate sites after infection. Also, if you mirror the software as a courtesy, you´ll run into interesting copyright issues. Pete
On Fri, 13 Feb 2004, Leo Vegoda wrote:
Yes, that is a little bit stickier of an issue, IFF your goal is to somehow continue to provide the would-be spammer with the ability to send traffic to the net, provided it doesn't transit your mail server. I feel that you're overlooking the simple solution. Blocking the entire account so they can't access anything is the proper response to a spamming incident.
If you block the entire account then the user can't use the account to download the updates your Abuse Team will responsibly want to point him/her at. If you want to lose the customer then that's your business. If you want to keep the customer, helping them fix their mistakes is probably a painful and thankless task - but important and useful to the whole Internet community.
What about http://www.nanog.org/mtg-0402/gauthier.html After seeing that presentation, I wondered if an ISP could get away with something similar. Eric has the advantage of being the monopoly service provider for the dorms. ---------------------------------------------------------------------- Jon Lewis *jlewis@lewis.org*| I route Senior Network Engineer | therefore you are Atlantic Net | _________ http://www.lewis.org/~jlewis/pgp for PGP public key_________
On Fri, 13 Feb 2004 at 5:14pm jlewis@lewis.org wrote:
What about http://www.nanog.org/mtg-0402/gauthier.html
After seeing that presentation, I wondered if an ISP could get away with something similar. Eric has the advantage of being the monopoly service provider for the dorms.
I know of at least one ISP that does similar, Onramp.net in Austin TX. I'm a corporate IT Mgr and one of my remote users is an Onramp customer that had ancient NAV on his personal PeeCee and caught whatever worm was in vogue a few months back. He is not a particularly computer savvy person, but he is not a luser either. He was quite pleasantly surprised at the service, once he realized what was going on. -- Joseph F. Noonan Rigaku/MSC Inc. jfn@msc.com
On Fri, 13 Feb 2004, Leo Vegoda wrote:
You wrote:
[...]
Yes, that is a little bit stickier of an issue, IFF your goal is to somehow continue to provide the would-be spammer with the ability to send traffic to the net, provided it doesn't transit your mail server. I feel that you're overlooking the simple solution. Blocking the entire account so they can't access anything is the proper response to a spamming incident.
If you block the entire account then the user can't use the account to download the updates your Abuse Team will responsibly want to point him/her at. If you want to lose the customer then that's your business. If you want to keep the customer, helping them fix their mistakes is probably a painful and thankless task - but important and useful to the whole Internet community.
RFC1918 is your friend, as is making internal copies of windowsupdate patches and virus removal tools. But even then, I would block 100% of access until we establish customer contact and are sure that the issue will be dealt with. Then, I would re-enable them on RFC1918 space, assist them in rectifying their problem, and then re-enable the rest of their account. This doesn't result in lost customers. This results in appreciative customers, even if they were blocked when they had the problem. If you don't block them, most people will never know until they've spewed gigs. Andy --- Andy Dills Xecunet, Inc. www.xecu.net 301-682-9972 ---
You could use AOL's tactic and transparent proxy all outbound port 25 traffic. Then it'd be a relatively simple matter to add mr. spammer's ip to a hosts.deny. If you were really big-brother, you could do real-time Beaysean scanning to identify "suspicious" hosts. -Ejay
-----Original Message----- From: owner-nanog@merit.edu [mailto:owner-nanog@merit.edu] On Behalf Of Dan Ellis Sent: Friday, February 13, 2004 11:55 AM To: Andy Dills Cc: nanog@merit.edu Subject: RE: SMTP relaying policies for Commercial ISP customers...?
Andy, These are exactly my concerns, and exactly what I feel I'm
going to hear from the staff and the customers. I am going to go back and make sure there isn't a "better" solution.
Thanks for the input.
The issue we have as a dynamic IP broadband provider is that it's a royal pain to shutdown a user - especially in regards to just mail. Lets say we have a spammer and a script detects it. We then have to track him back to the MAC address of the modem, lookup that MAC in the customer DB, shutdown
his access and then reset the modem. And at the end, he loses all access, not just mail. With AUTH we can just stop mail access. Yeah, sure we could try to push some access list to the modem itself, blocking mail, but those modems are so flaky to start, it'll never work reliably. Can't just block the IP on the mail server because the user will or could just get a new IP, and then you are blocking a legit user.
I'm still not sure if the norm is for providers to let t1+
customers relay. I have multiple OC3's and 12's from AT&T, MCI,... Will they let me relay off their servers without SMTPAUTH? Probably not.
As always, comments welcome.
-- Daniel Ellis, CTO, PenTeleData (610)826-9293
"The only way to predict the future is to invent it." --Alan Kay
-----Original Message----- From: Andy Dills [mailto:andy@xecu.net] Sent: Friday, February 13, 2004 12:35 PM To: Dan Ellis Cc: nanog@merit.edu Subject: Re: SMTP relaying policies for Commercial ISP customers...?
On Fri, 13 Feb 2004, Dan Ellis wrote:
1) Residential Policy: Enable SMTPAUTH and disallow relaying unless the customer has a valid username/password. If
for a mailbox, you don't get to relay outbound. This should not break anything except those residential accounts that *should* be commercial anyway.
2) Broadband commercial: This is the difficult one. These are the customers that aren't big enough to rightfully run
you're not paying their own mailserver,
but they are big enough to have roaming users on their
networks (coffee
shops, branch offices, hotels, SOHO....). They expect
for either their mailserver or for all their various PC's. At the same time, they don't have many, if any mailboxes through
thought is that they should ONLY be allowed to relay via SMTPAUTH by using a residential mailbox login/pass OR they need to
relaying service the ISP. My purchase a
commercial relay service (expensive because of the openness of it) for their IP space.
3) T1+ : These customers should not be allowed to relay unless they purchase (expensive) relay services for their IP space. Of course, they can always use a residential mailbox, but will have to use SMTPAUTH for it and will be restrained by the same policies residential mailboxes have (low tolerance tarpitting,...).
While the amount of effort you put into this so far is commendable, I really think you're barking up the wrong tree.
At the end of the day, what have you done, besides annoy
your customers
and increase the load on your support staff?
I don't really see what you're suggesting being anything
effort, solving the wrong problem.
For any responsible ISP, the problem is the spam coming into your mailservers, not leaving. As long as you quickly castrate
other than a huge the people who
do relay spam through you, you're not going to have an egress spam problem.
Since you seem to have countless hours to invest in this
better off writing a log parser to identify WHEN somebody is relaying spam through you, so you can react.
Something else I've seen implemented is rate limiting. Keep
problem, you'd be track of the
number of messages sent by an IP over a variable amount of time and implement thresholds.
I'd love to hear some of the conversations you have with
customers, when you tell them they have to pay for "(expensive) relay services" to send mail through your mail server. How many times will they laugh before hanging up on you? :)
That's like the IRS trying to charge you for the
your leased line forms...
And I'd also like to see the looks on your technical
when you tell them they need to assist your ENTIRE USER BASE in switching to authenticated SMTP :)
And then you have to deal with the customers who have MTAs
support authenticated SMTP...and on and on.
Whenever the solution is more expensive than the
support staff's faces that don't problem, you need to go
back to the drawing board.
Andy
--- Andy Dills Xecunet, Inc. www.xecu.net 301-682-9972 ---
On 2004-02-13T15:30-0600, Ejay Hire wrote: ) You could use AOL's tactic and transparent proxy all ) outbound port 25 traffic. Then it'd be a relatively simple ) matter to add mr. spammer's ip to a hosts.deny. If you were You may also need to filter inbound packets with a source port of 25, or any other ports you capture. As I believe has been mentioned here before, some spammers may use a dialup account just for its IP address, collecting return packets on the dialup interface but sending the actual content through some higher-bandwidth, unfiltered pipe. Filtering what goes out over the dialup account would be largely ineffective in this case, as nothing actually needs to be sent through that interface for the transmissions to succeed. -- Daniel Reed <n@ml.org> http://naim-users.org/nmlorg/ http://naim.n.ml.org/ "True nobility lies not in being superior to another man, but in being superior to one's previous self."
participants (8)
-
Andy Dills -
Dan Ellis -
Daniel Reed -
Ejay Hire -
jlewis＠lewis.org -
Joseph Noonan -
Leo Vegoda -
Petri Helenius