issue with email delivery going through Cloudron mailing lists.

[avatar1024]

Hello,

On one of my Cloudron, email delivery fails to Gmail address but this ONLY when the email goes through a Cloudron mailing lists and only when sent from particular addresses.

Currently on Cloudron 8.2.3 but the issue has been there fore a while (past 8 months on and off).

What is happening:

If I send emails sent from a mailbox on that Cloudron (test@mydomain.coop), emails are delivered fine to any addresses, including gmails.

I have a few Cloudron email lists where in them there are some people with gmail addresses.

If someone with a gmail or outlook addresses address send through those lists, emails are delivered fine to everyone with no delay.

When I send an email to those lists from my posteo email address, email are delivered fine to everyone, except those on gmail address when I get an error type:

Delivery failure, will retry in XYZs. Upstream error: 421 4.7.28 Gmail has detected an unusual rate of unsolicited mail. To protect 4.7.28 our users from spam, mail has been temporarily rate limited. For 4.7.28 more information, go to 4.7.28 https://support.google.com/mail/?p=UnsolicitedRateLimitError to 4.7.28 review our Bulk Email Senders Guidelines.
SRS0=2bd9=S6=posteo.net=me@mydomain.coop

This also happen with people sending from protonmail and other non-mainstream email providers.

When sending email from my posteo address directly to the people with gmail addresses (without going through a Cloudron list) email are going through fine. The same is true for people with protonmail addresses and the other less mainstream email providers.

I tested the Cloudron domain on https://mxtoolbox.com and https://multirbl.valli.org/ and all looks good.

Any clues on what might be going on?

Edit: see the additional testing below which may give some clues, and specifically that something seem to be up specifically with the Cloudron mailing list function with regards to Gmail email delivery as it works fine with other (filter based) implementations of email forwarding.

[avatar1024]

I should add: I created another list with a range of email addresses (posteo, protonmail, gmail, etc...), with only one gmail. With this one, all emails are going through just fine, not matter who is sending.
Email lists where it's not working have several gmail addresses in them (5 and 7).

[avatar1024]

And sometimes the error message is this:
Upstream error: 421 4.7.28 Gmail has detected this message exceeded its quota for sending 4.7.28 messages with the same Message-ID. To best protect our users, the 4.7.28 message has been temporarily rejected. For more information, go to 4.7.28 https://support.google.com/mail/answer/188131

[jdaviescoates]

@avatar1024 said in issue with email delivery going through Cloudron mailing lists.:

For 4.7.28 more information, go to 4.7.28 https://support.google.com/mail/?p=UnsolicitedRateLimitError

Based on what it says there and what you've said here my guess is that it thinks you're too rapildy emailing the 5 or 7 gmail addresses in the groups where this is an issue. It seems like google thinks you're very rapidly separately emailing those 5 or 7 people rather than realising it's one email sent to a list.

But I've no idea what you could do about it, if anything

[avatar1024]

@jdaviescoates Thanks! I wonder if anyone can reproduce this to see if it is a general issue with Gmail, or something specific to my server.

Also it seems weird that would happen with only 5 or 7 people. I can easily imagine (and I'm sure I did) sending a personal email to 5+ recipients that have gmail addresses without it causing an issue.

@staff what do you reckon about the above problem? Is there anything that could be done to mitigate this?

Thank you!

[avatar1024]

Ok so I've done additional testing:

1. I created a brand new list like earlier with a few people but only one gmail address: everything works fine.
2. I added 5 more gmail addresses: errors started to show up
3. I created a mailbox and in roundcude within which I created a filter that forwards all emails to exactly the same 6 gmail addresses + the non gmail addresses as in 2.: everything works fine!!

So the issue really ONLY happens when using the mailing list function.

Sadly 3. is not really a workaround as those lists with issues are closed lists and so I would need to set a rule to the filter so it only allows emails from those people (this would work to reproduce the closed list feature of Cloudron but it would be a tedious workaround and not easily self managed by the people on this Cloudron as they aren't very tech savy...they're ok with Cloudron list feature but probably not with going into mailboxes, set/change filters etc.).

[girish]

I think this is related to SRS rewriting for mailing lists. IIRC, gmail does not like SRS Other vendors like outlook/hotmail want SRS. I guess the mail sever can maintain some sort of a list of who supports SRS and who doesn't.

[avatar1024]

@girish Hi Girish, thanks for looking into this. That could be it, although it looks like when I do the redirect filter with roundcube to replicate the email list behaviour there is also a SRS rewrite and emails are going through fine.
I could send you the event logs if you want to compare the two?

[girish]

@avatar1024 good point about redirection not being affected! I will add this into the next release checklist.