issue with mailing list delivery when using external SMTP server

[girish]

@avatar1024 external relay services will only relay addresses that you added to them explicitly. So if you added foo.com into postmark, postmark will only relay email address which have From as *@foo.com .

The idea of mail forwarding is that the From address has to be that of the original. So, the From address has to set to say someone@posteo.com . Postmark will reject these emails (correctly).

So to summarize: domain-locked relays and keeping the original sender on forwards/lists do not go together. You can relay or you can transparently forward third-party mail, not both. There's nothing Cloudron can do about this from what I know.

[avatar1024]

@girish said:

@avatar1024 external relay services will only relay addresses that you added to them explicitly. So if you added foo.com into postmark, postmark will only relay email address which have From as *@foo.com .

The idea of mail forwarding is that the From address has to be that of the original. So, the From address has to set to say someone@posteo.com . Postmark will reject these emails (correctly).

So to summarize: domain-locked relays and keeping the original sender on forwards/lists do not go together. You can relay or you can transparently forward third-party mail, not both. There's nothing Cloudron can do about this from what I know.

Thanks for the explainer @girish. Does that means one cannot use an external relay to replace the built in SMTP server if we use mailing lists (or the mailbox + forward implementation in Cloudron 10) - given most likely senders and mailing lists members with use random email providers?

[girish]

@avatar1024 said:

Does that means one cannot use an external relay to replace the built in SMTP server if we use mailing lists (or the mailbox + forward implementation in Cloudron 10) - given most likely senders and mailing lists members with use random email providers?

Yes, with a typical smart host / relay you cannot keep the original sender on list/forward delivery to Gmail/Posteo/etc.

I want to mention that this is for the forwarding feature. Forwarding requires From address to be preserved. A mailing list behaves differently. It rewrites From/Reply-To etc and makes itself the originator of the email. This feature was never implemented in Cloudron. The forwarding feature was incorrectly labeled as mailing list and this misnaming is fixed in Cloudron 10.

I guess we have to look into Distribution lists/mailing lists for the next releases, if you are interested in this. But the From address will change, not sure if it will work for your use case. It's usually meant for group@example.com or list@example.com style workflows.

[avatar1024]

@girish said:

@avatar1024 said:

Does that means one cannot use an external relay to replace the built in SMTP server if we use mailing lists (or the mailbox + forward implementation in Cloudron 10) - given most likely senders and mailing lists members with use random email providers?

Yes, with a typical smart host / relay you cannot keep the original sender on list/forward delivery to Gmail/Posteo/etc.

I want to mention that this is for the forwarding feature. Forwarding requires From address to be preserved. A mailing list behaves differently. It rewrites From/Reply-To etc and makes itself the originator of the email. This feature was never implemented in Cloudron. The forwarding feature was incorrectly labeled as mailing list and this misnaming is fixed in Cloudron 10.

I guess we have to look into Distribution lists/mailing lists for the next releases, if you are interested in this. But the From address will change, not sure if it will work for your use case. It's usually meant for group@example.com or list@example.com style workflows.

Thanks Girish, and yes a mailing list feature will be useful for some of my use case.

I guess the point here is that it's a shame there isn't a way to use an external relay as a blanket replacement (i.e. covering all email features including forwarding) to the built-in SMTP server cause those services have added features to ensure reliable delivery (say when the server has a bad IP rep and gets regularly blocked notably by Microsoft stupid IP range blacklist approach).

[msbt]

Just chiming in here because I ran into the same problem (i.e. a formerly working Postmark email forwarder for a group of externals is not working anymore, because none of them use the cloudrons' domain). What's the current solution, set up a separate mailinglist app? Or would switching to the internal mailserver solve it?

[girish]

@msbt does postmark have more info on why it is rejecting the email?

so from all my research on this, forwarding via a smart host (especially postmark) is not solvable. Postmark doesn't allow the envelope from and the email from addresses to mismatch. Fundamentally, this means forwarding will not work the way you want.

[msbt]

@girish but why was it working on Cloudron 9? It only stopped after upgrading to 10, when addresses got migrated from mailinglist to forwards.

That's the odd thing, there's not really a proper error message, no suppression in Postmark itself. In the mail logs it just says [cloudron] final rcpt list is ["<group@example.com>","<cc1@somesite.com>","<cc2@gmail.com>"]. The mail arrived at the two cc'ed addresses, but the group@example.com forwards never make it. Maybe because LMTP bypasses the filters?

[girish]

@msbt internally, the behavior of the previous mailing list and current forwarding is the same. It was only a rewording to clarify what the feature is doing. So, I think we have to investigate further why it has stopped working in Cloudron 10.

Don't you see anything on the postmark logs? You should see three separate emails coming to postmark (the to and the two ccs). You should also see the 3 events in the cloudron eventlog. Do you see a mail to group@example.com ?

[msbt]

@girish no, postmark never sees the group@example.com because it's internal mail

[girish]

@msbt ah, that's why you said LMTP! And nothing in Cloudron eventlog?

@james can you help reproduce this please?

[msbt]

@girish in Cloudron everything looks normal, in the last row it lists the external group mailbox, internal team and the 2 external cc'ed users (cut off), the internal mails get saved, the cc'ed ones sent, but the group never attempts to forward the mails.

[james]

Hello @msbt
I need to understand the set up first to reproduce it.

1. domain in Cloudron e.g.: cloudron.dev
2. mail settings for cloudron.dev smart host configured to use postmark
3. 2x mailboxes on Cloudron for group@cloudron.dev and team@cloudron.dev
   3a. (group|team)@cloudron.dev are configured to forward to e.g.: someinbox@gmail.com
4. a mail is sent to (group|team)@cloudron.dev and 2x cc e.g.: cc1@gmail.com and cc2@outlook.com

Resulting in:

• cc1 and cc2 delivered
• group and team saved locally on Cloudron, but never forwarded to someinbox@gmail.com

Did I get this right?

[james]

Hello @msbt
I have tested the following set up on Cloudron 10.0.4:

• domain cloudron.dev smart host configured for postmark
• local inbox groupone@cloudron.dev owned by a group named groupone
• local inbox grouptwo@cloudron.dev owned by a group named grouptwo

Forward settings:

• groupone@cloudron.dev forward settings to grouptwo@cloudron.dev and external@gmail.com
• grouptwo@cloudron.dev forward settings to external@outlook.com

Sending a mail to groupone@cloudron.dev is delivered to:

• groupone@cloudron.dev
• grouptwo@cloudron.dev
• external@gmail.com
• external@outlook.com

From this set up I was not able to reproduce your issue.

[msbt]

@james thanks for testing! In my setup the groupone@ is a regular user with 40 forwarding addresses and grouptwo@ is a shared mailbox without any forwards, but other than that you're right.

So the only difference is that groupone is owned by a single user, not a group and grouptwo is a shared mailbox with no forwards.

I can't imagine how single user vs group owners would make a difference. Did you chance anything else, like FROM address validation? Keep a copy in the inbox? Restrict senders?

[james]

Hello @msbt

All default.

[msbt]

@james can you try again without the "Keep a copy in the inbox", that's the only difference I'm seeing

edit: and maybe remove grouptwo from forwarding as well, but again, no idea how that could make a difference

[james]

Hello @msbt
No difference. Still working just fine.

[girish]

@msbt said:

@james thanks for testing! In my setup the groupone@ is a regular user with 40 forwarding addresses and grouptwo@ is a shared mailbox without any forwards, but other than that you're right.

This stood out. There is a cap of 64 forwards in the code. Could you be hitting this limit? Specifically sieve_max_redirects is 64 . I thought this was a very high number, may be not?

[msbt]

@girish unsure, it really is 40. Would there be something in a log and if so, where?

[girish]

@msbt the errors if any should be in /run/dovecot/dovecot.log or the main docker logs -f mail . You can also check if the mail is stuck in the mail queue at /app/data/haraka-queue (these are mails which are being "retried") .