Email Relaying Problem

[PetrolTed]

One of my customers is getting some of his emails rejected. e.g.

Your message did not reach some or all of the intended recipients.

Subject: Test

Sent: 24/11/2003 11:03

The following recipient(s) could not be reached:

'********@**********' on 24/11/2003 11:03

550 5.7.1 <********@**********>... we do not relay


The mails are being sent via my server so it's not my server rejecting the message. Why would a server downstream claim that we're trying to relay?

[roop]

Ted,

Some ISP's now intercept any SMTP on port 25 and either block it or re-route it through their own SMTP servers (Freeserve do the re-route for sure). It could be your customer's ISP has decided to block SMTP traffic intended for any other servers than it's own by re-routing and blocking. It's all in aid of anti-spam of course.

If Freeserve is anything to go by they seem to randomly change things without warning. There's stuff on the web about this that a quick google will show up.

Roop

[Plotloss]

Sounds like you have fallen foul of some sort of antispam filter.

Not saying your mails are spam at all, more commenting on the inelegant solutions being prescribed for this problem...

[PetrolTed]

Roop said:

Some ISP's now intercept any SMTP on port 25 and either block it or re-route it through their own SMTP servers (Freeserve do the re-route for sure).

Blimey, that's shit. Surely they can't do that?

They're using BT ADSL - anyone have any experience there?

I don't think it's a spam detection false positive as I don't have the same problems and I'm sending from the same server/IP.

[roop]

Yep. Cackstation zebra. Try opening a command prompt while connected to the ISP in question and telnetting to your SMTP server on port 25 and see what welcome message comes up. You'll know if it's your box or not then.

When I tried this on FS I expected to get *******.ik.com at 62.173.103.*** and got some FS SMTP server instead.

Roop

PetrolTed said:

Roop said: Some ISP's now intercept any SMTP on port 25 and either block it or re-route it through their own SMTP servers (Freeserve do the re-route for sure). Blimey, that's shit. Surely they can't do that? They're using BT ADSL - anyone have any experience there? I don't think it's a spam detection false positive as I don't have the same problems and I'm sending from the same server/IP.

[PetrolTed]

Did you find a workaround Roop?

[roop]

'fraid not Ted. I called FS helpdesk and paid 50p/min to speak to a schmuck with a script who *would not* escalate the issue to someone else no matter what and kept telling me it was a problem with my Outlook Express settings. FFS...! Later that day it just started working again - admittedly via FS SMTP servers, but that's no problem so long as it works.

The only option I can think of is to switch the SMTP port to something other than 25 and request your customers reconfig their mail clents - either that or switch ISP.

I wouldn't care if the ISP's did this *IF* it was mentioned in T&C's or anywhere else, but it's not - ISP's keep this thing very low profile. I know it's done for the benefit of less spam etc but it royally knackers those of us who provide alternative email services.

Good luck - don't hesitate to mail me with any questions or whatever.

Roop

PetrolTed said:

Did you find a workaround Roop?

[PetrolTed]

Well it's not that. I've had them check it out via telnet and it's definitely my server that they're going out on.

I don't understand why a third party server should be generating 550 messages. Could it be some inconsistency in the mail address/reply address etc?

[roop]

Hrm, you're server's not doingf any ORDB lookups or similar - you haven't been blacklisted...?

Odd as mail sending for one of my domain packed up last week in similar circumstances, I had to add the domain to a whitelist before it worked.

Roop

PetrolTed said:

Well it's not that. I've had them check it out via telnet and it's definitely my server that they're going out on. I don't understand why a third party server should be generating 550 messages. Could it be some inconsistency in the mail address/reply address etc?

[craigalsop]

PetrolTed said:

Why would a server downstream claim that we're trying to relay?

Because the domain of the email address is non-local to that server? This could be down to either misconfiguration of the email server, or the MX record in the DNS table could be incorrect.

Am I right in thinking that this message is coming from a bounce at the downstream server, rather than your server?

[PetrolTed]

craigalsop said:

Am I right in thinking that this message is coming from a bounce at the downstream server, rather than your server?

That's what I'm trying to establish now. Thinking about it, it may be my server - I was assuming it wasn't. I insist on a POP before an SMTP and it's possible that the user isn't doing that. I've just turned on logging to see if that tells me.

[Graham]

IS it your server on the BT ADSL line?

i've got a customer with a similar problem. their server carnt send mail to 2 of there employees. It turns out the peeps that handle the employees mail ( apparently they handle things like tescos.net ect) block anything comming from a BT ADSL ip range as spam... point blank and bounce it...

G

[craigalsop]

PetrolTed said:

That's what I'm trying to establish now. Thinking about it, it may be my server - I was assuming it wasn't. I insist on a POP before an SMTP and it's possible that the user isn't doing that. I've just turned on logging to see if that tells me.

You should also be able to get some information from the message itself, if you look at the full message source, it should have all of the "Received: from" lines, with the relevant IPs
It could well be an authentication thing due to POP before SMTP not being performed, as this will be the test that says "this user is local, let them relay to the outside world", rather than the more usual <user@localdomain> and/or IP range

>> Edited by craigalsop on Monday 24th November 16:02

[JamieBeeston]

check your logs, as you say.

Also, check the mail, as usually there will be more info in that, in an attachment, specifically which server bounced it.

Feel free to forward the mail if you need.

[JamieBeeston]

also, does he get this message to everyone, or just some people.

If its everyone, then it would point to an issue with you.

if not, it might be someone has a poor forwarding / MX setup at the destination.

[davidd]

Mail relaying is a complete arse, bloody spammers making our lives difficult.

If you get stuck and are allowed, forward me the email and I'll have a look.

Cheers

D.

[PetrolTed]

Just waiting for some feedback from the client. My money's on them using email differently to how I expected and not doing the POP before SMTP required.

[JamieBeeston]

PetrolTed said:

Just waiting for some feedback from the client. My money's on them using email differently to how I expected and not doing the POP before SMTP required.

But surely if they send and receive, then technically the first time they send, it will fail.. but they should then POP... and the next time it will go thru.

But, like you say, its invariably some issue where they are doing something 'unnatural'

Oh.. we forgot, we migrated to outlook 2003.... would that make a difference

;P

[davidd]

PetrolTed said:

Just waiting for some feedback from the client. My money's on them using email differently to how I expected and not doing the POP before SMTP required.

Are they authenticating to the outgoing (smtp ) server?

D.