Undelivered Mail Returned to Sender

baspax1

Hi , Im using the latest version of mailcow,
i have my own domain that is worked more than one year correctly, but now i have 2 days that i cant send mails from my domain to Gmails.
I get error like:

This is the mail system at host mailserver.netgen.gr.

I'm sorry to have to inform you that your message could not
be delivered to one or more recipients. It's attached below.

For further assistance, please send mail to postmaster.

If you do so, please include this problem report. You can
delete your own text from the attached returned message.

                   The mail system

<baspax1@gmail.com>: host gmail-smtp-in.l.google.com[173.194.79.27] said:
    550-5.7.1 [38.242.140.28      19] Our system has detected that this message
    is 550-5.7.1 likely suspicious due to the very low reputation of the
    sending 550-5.7.1 domain. To best protect our users from spam, the message
    has been 550-5.7.1 blocked. Please visit 550 5.7.1
    https://support.google.com/mail/answer/188131 for more information.
    w6-20020a17090633c600b00987d26a0998si12388727eja.455 - gsmtp (in reply to
    end of DATA command)

i didnt change anything on my setup, and look like everything good about dns setup and mail-tester
https://prnt.sc/_B0sQe3jtdYi
https://prnt.sc/Nxo6ccwrZpPN

Please what else can i do to can send in gmail users?

esackbauer

Did you follow the link in that SMTP message? And registered your domain with the Postmaster Tools to gmail?

baspax1

esackbauer

I thought that owning the domain, like netgen.gr, covered everything. However, when I directly input mailserver.netgen.gr, it worked! I hadn’t considered that it would make a difference!

https://prnt.sc/E-EnA8qvDqvW

baspax1

baspax1
Hi again today i try again , and i get the same error:
This is the mail system at host mailserver.netgen.gr.

I’m sorry to have to inform you that your message could not
be delivered to one or more recipients. It’s attached below.

For further assistance, please send mail to postmaster.

If you do so, please include this problem report. You can
delete your own text from the attached returned message.

               The mail system

baspax1@gmail.com: host gmail-smtp-in.l.google.com[173.194.69.26] said:
550-5.7.1 [38.242.140.28 19] Our system has detected that this message
is 550-5.7.1 likely suspicious due to the very low reputation of the
sending 550-5.7.1 domain. To best protect our users from spam, the message
has been 550-5.7.1 blocked. Please visit 550 5.7.1
https://support.google.com/mail/answer/188131 for more information.
u10-20020a056402110a00b0051bfb6074a5si12229112edv.84 - gsmtp (in reply to
end of DATA command)

Must do something additional?

esackbauer

https://docs.mailcow.email/prerequisite/prerequisite-dns/#dkim-spf-and-dmarc
Your DMARC entry says “none” instead of “reject”.

Also try the Gmail Troubleshooter.

baspax1

esackbauer
i change to reject , but not helped, maybe must whait , also i send to gmail troubleshooter to get an asnwer

esackbauer

baspax1
DNS changes take some time if not hours to be replicated. Also Google says that reputation score is changed slowly.

jimmy_jummy

I don’t know if Gmail uses one of these, but maybe you should try to get delisted from the 7 blacklists on which your IP is on:

https://multirbl.valli.org/lookup/38.242.140.28.html

BTW: Contabo has lots of IPs with bad reputation and you’re probably never gonna make it directly into the inbox of the recipients. Better use a relay service like smtp2go.

baspax1

jimmy_jummy
I used contabo because was cheap way, instead of hetzner or other servers, I knew that has some issues with blacklist ip , but i give them a second change, Now i see that i have the same problems and he forces me to transfer to zoho if i dont find solution..
Can you help me please with that? what must do with smtp2go? is it difucult or cost too much extra?
I want to avoid the server trasnfer and the resetup of mailcow to another, so the smt2go maybe do the job for my problem?

esackbauer

Yes, always check the blacklists before posting here…
I was assuming that people who run mail servers are aware of it, because even the documentation mentions it:
https://docs.mailcow.email/troubleshooting/debug-common_problems/#i-can-receive-but-not-send-mails

Select your hosting wisely or better use a relay service. If you don’t want to, try to get your own whole subnet, even if it costs extra. I had once a /30 subnet, and I had absolutely never problems. Now I am using a relay service, because I changed providers.

jimmy_jummy

baspax1

In fact smtp2go is really easy to setup. First you open an account there (free plan includes up to 1000 mails per month).
You need to create an SMTP user and you need to setup your domains as “sender domains”. For that you need access to your domain DNS entries, because you have to create some CNAME entries. Please follow the guide on smtp2go.com.

After you save the details in Mailcow under System -> Configuration -> Routing -> Transport maps.
It should look like this:

If you have lots of trouble to get your mails delivered, you could try to place a wildcard under “destination” so that ALL outgoing mails will be relayed to smtp2go. Otherwise you can start to use the relay for single domains like gmail.com, outlook.com etc.

You can find some more details regarding relayhost here:

https://docs.mailcow.email/en/manual-guides/Postfix/u_e-postfix-relayhost/?h=transport

Good luck!

baspax1

jimmy_jummy
I want to thank you for help the steps was very easy, i change the outgoing to that service and all works perfeclty, the limit of 1k mails is enough for me
My mail after that sends again to Gmail users!

Thanks again the community for help.

jimmy_jummy

baspax1

You’re welcome. I’m glad you were able to solve your problems.

BTW: if you re-think about your situation at Contabo one day, I can highly recommend the new Hetzner ARM64 tariffs which offer very good value for the money. For example:

I have this one since 4 weeks and my Mailcow (and several other services) are running without any problems. I never had any downtime or other trouble and my IP is absolutely clean. I can even deliver directly to Microsoft which is - honestly speaking - a miracle. ;-)

I know Hetzner cost two bucks more, but it’s really worth the price. You would never want again a low-cost provider like Contabo.

Good luck and all the best…