BT emails delivery issue

[JimKillock]

BT Categorisation report that:

"We have recently noticed that when we reply back to emails from blocked.org.uk we intermittently received undeliverable messages from the mail servers. I have attached a few mails whereby we have replied back and received either a Delivery Delayed or Undeliverable."

Can you check to see what has happened?

EDIT

Change how forwarding works, so that we work as a "man in the middle" changing the From and Reply to as @blocked.org.uk for the blocked user and BT, eg:

1. Send reports to BT as [email protected]
2. BT returns email to [email protected]
3. We forward BT email using a From: header that belongs to us eg [email protected]
4. User replies to the same From: header, eg [email protected] and we route that back to [email protected] via blocked.org.uk, sending to BT using From: [email protected] ;
5. The BT reply to should consistent with the original review request, eg [email protected] so any threads can be preserved.

[JimKillock]

You will have seen the emails and chat: can you change the way we forward emails so that the email:

1. Send reports to BT as [email protected]
2. Uses a From: header that belongs to eg [email protected]
3. Allows the user to reply to the same From: header, eg [email protected] and route that back to [email protected] via blocked.org.uk, send to BT using [email protected] ;
4. The BT reply to should consistent with the original review request so any threads can be preserved.

It may make sense to treat all of the response emails in this way to avoid any other DMARC issues?

[dantheta]

We can do (1) and (2) pretty easily, we'd just need to set up a fixed reply- alias for each of the ISPs. Capturing subsequent ISP replies (3) is slightly harder, as we won't have the original ISP report alias available after their reply in (2), since that reply will have used the user's own email address. Looking up the correct alias based on the subject line and ISP should be possible.

[JimKillock]

I think I see what you mean!

Nevertheless with (3) the user would reply with their own email address, rather than [email protected] but the reply-to, eg [email protected] would be the same as the email sent "as if" BT, so should match that way? You'd need a unique "User Alias" and a unique "BT Alias" on our end?

[JimKillock]

(I've edited the comment and the task to make this a bit clearer. I think my descrption wasn't quite clear.)

[JimKillock]

Does this make sense @dantheta ? We should be able to play 'man in the middle' and rewrite the "from" in both directions, in essence.

[dantheta]

Yep - I'm working on the required postfix configuration at the moment.

…

On Fri, 19 Feb 2021, at 12:09, JimKillock wrote: Does this make sense @dantheta <https://github.com/dantheta> ? We should be able to play 'man in the middle' and rewrite the "from" in both directions, in essence. — You are receiving this because you were mentioned. Reply to this email directly, view it on GitHub <#116 (comment)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AADBG7K5NDJO6JVJT7ABV63S7ZIIHANCNFSM4XYEC54Q>.

[dantheta]

The site now adds a reply-isp-xxxxxx From: address to email coming from the ISPs. BT still include a reply-to header in their outgoing mail, so we might not be able to capture all of the user -> ISP replies (though there haven't been many of those).

It's been tested reasonably well, but if it causes any problems we can revert the change quite easily.

[JimKillock]

Sounds good Daniel; can we consider changing the reply-to header as well?