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Rejecting specific mailboxes with catchall on

Community Veteran
Posts: 26,345
Thanks: 600
Fixes: 8
Registered: 10-04-2007

Rejecting specific mailboxes with catchall on

I like a number of other people have the catch all on because I use unique email addresses when signing up to websites and prefer not to have to wait before signing up to be certain that a newly created alias is ready for use. This means that all mail to my domains is accepted by the IronPort boxes, including spam for addresses harvested in the WebMail incident which are now not used. Using the redirect to blackhole is the solution offered by Plusnet.
The problem I have is that there is still a possibility that for some of the addresses, genuine email could be sent to the address. When blackhole is used I don't know a genuine email was received and the sender doesn't get a rejection so they think it was delivered; blackholing is therefore not a viable alternative.
I've been experimenting with an alternative method. Instead of blackholing (redirecting to blackhole@abuse.plus.com) I redirect to email.blocked@mailbox.inv. Now any mail received gets bounced with
The following message to <spammedmailbox@username.plus.com> was undeliverable.
The reason for the problem:
5.1.0 - Unknown address error 550-'REJECTED: Cannot route message'
Reporting-MTA: dns; mx.ptn-ipin03.plus.net
Final-Recipient: rfc822;spammedmailbox@username.plus.com
Action: failed
Status: 5.0.0 (permanent failure)
Remote-MTA: dns; [212.159.9.1]
Diagnostic-Code: smtp; 5.1.0 - Unknown address error 550-'REJECTED: Cannot route message' (delivery attempts: 0)

which means that the sender of a genuine message gets to know it was not delivered.
The immediate reaction of some people to this idea will be 'backscatter', but with the IronPort system (especially with 'edge filtering' aka blatant spam blocking on) very few spam emails get to the stage where they are rejected so the volume of email being backscattered will be minimal.
jelv (a.k.a Spoon Whittler)
   Why I have left Plusnet (warning: long post!)   
Broadband: Andrews & Arnold Home::1 (FTTC 80/20)
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6 REPLIES
Community Veteran
Posts: 38,214
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Registered: 15-06-2007

Re: Rejecting specific mailboxes with catchall on

jelv,
Can you give a bit more information about email.blocked@mailbox.inv
Is this something one needs to sign up to or is it open to anyone
Community Veteran
Posts: 26,345
Thanks: 600
Fixes: 8
Registered: 10-04-2007

Re: Rejecting specific mailboxes with catchall on

It's a made up email address that doesn't exist (in fact the TLD .inv doesn't exist). You can use any address you want but need to make sure that it is for a non-existent domain - check using nslookup. E.g.
C:\Documents and Settings\John>nslookup -type=mx nosuchuser.plus.com
Server:  localhost
Address:  127.0.0.1
*** localhost can't find nosuchuser.plus.com: Non-existent domain

So using go.away@nosuchuser.plus.com would work just as well.
jelv (a.k.a Spoon Whittler)
   Why I have left Plusnet (warning: long post!)   
Broadband: Andrews & Arnold Home::1 (FTTC 80/20)
Line rental: Pulse 8 Home Line Rental (£13/month)
Mobile: iD mobile (£4/month)
Community Veteran
Posts: 38,214
Thanks: 909
Fixes: 54
Registered: 15-06-2007

Re: Rejecting specific mailboxes with catchall on

so bugger@bugger off.com might be even better  Grin
Community Veteran
Posts: 26,345
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Registered: 10-04-2007

Re: Rejecting specific mailboxes with catchall on

Wouldn't recommend it - off.com is a valid domain.
jelv (a.k.a Spoon Whittler)
   Why I have left Plusnet (warning: long post!)   
Broadband: Andrews & Arnold Home::1 (FTTC 80/20)
Line rental: Pulse 8 Home Line Rental (£13/month)
Mobile: iD mobile (£4/month)
Community Gaffer
Community Gaffer
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Registered: 04-04-2007

Re: Rejecting specific mailboxes with catchall on

Well thought out solution jelv, I like it. As you've said, I can't imagine backscatter will be too much of an issue as IronPort's SBRL will put a stop to the vast majority of spam before it even gets to the mx.cores to be redirected.

Bob Pullen
Plusnet Products Team
If I've been helpful then please give thanks ⤵

Community Veteran
Posts: 26,345
Thanks: 600
Fixes: 8
Registered: 10-04-2007

Re: Rejecting specific mailboxes with catchall on

A couple of issues have appeared with this scheme:
1. Messages that are accepted but identified as spam will not get forwarded if you either have quarantine on or deliver to a different mailbox selected. (I see these so no genuine email could get lost)
2. I've seen a message accepted by IronPort but not identified as spam where the sender has faked the same email address as the from. The reject was identified as spam and was therefore handled as such. If it hadn't been identified as spam the sequence would have been:
Email comes in addressed to abc@myuser.plus.com with abc@myuser.plus.com as the from address and is redirected to email.blocked@mailbox.inv.
This is rejected and the rejection is sent to abc@myuser.plus.com which is then redirected to email.blocked@mailbox.inv.
This is rejected and the rejection is sent to abc@myuser.plus.com which is then redirected to email.blocked@mailbox.inv.
This is rejected and the rejection is sent to abc@myuser.plus.com which is then redirected to email.blocked@mailbox.inv.
This is rejected and the rejection is sent to abc@myuser.plus.com which is then redirected to email.blocked@mailbox.inv.
...
Presumably there is something in your system that detects such mail loops and eventually kills the messages. However, from my perspective it's all working fine so I'm not bothered about these potential loops.

Of course all of this is just because those of us with the catchall on don't have the ability to blacklist particular recipient addresses so that IronPort rejects the message at the time of the original connection in the same way it does for unknown addresses for people with the catchall off. See PUGIT 300 which was raised 19 Apr 2007.
jelv (a.k.a Spoon Whittler)
   Why I have left Plusnet (warning: long post!)   
Broadband: Andrews & Arnold Home::1 (FTTC 80/20)
Line rental: Pulse 8 Home Line Rental (£13/month)
Mobile: iD mobile (£4/month)