Sending Email not working

PiyushDesai

Priority	Message

10/29/2025, 06:57:19 PM info 81515100221: to=piyushdesai204@gmail.com, relay=alt2.gmail-smtp-in.l.google.com[192.178.209.27]:25, delay=1.2, delays=0.44/0/0.8/0, dsn=4.7.4, status=deferred (TLS is required, but was not offered by host alt2.gmail-smtp-in.l.google.com[192.178.209.27])
10/29/2025, 06:57:18 PM info 81515100221: replace: header Received: from 8136eef12f5b (mailcowdockerized-sogo-mailcow-1.mailcowdockerized_mailcow-network [172.22.1.248])??(Authenticated sender: piyush.a@getcollarup.com)??by mail.getcollarup.com (Postcow) wit from mailcowdockerized-sogo-mailcow-1.mailcowdockerized_mailcow-network[172.22.1.248]; from=piyush.a@getcollarup.com to=piyushdesai204@gmail.com proto=ESMTP helo=<8136eef12f5b>: Received: from [127.0.0.1] (localhost [127.0.0.1]) by localhost (Mailerdaemon) with ESMTPA id 81515100221??for piyushdesai204@gmail.com; Wed, 29 Oct 2025 18:57:18 +0530 (IST)
10/29/2025, 06:55:34 PM info 1BD0510004A: to=piyushdesai204@gmail.com, relay=none, delay=0.83, delays=0.44/0.01/0.38/0, dsn=4.4.1, status=deferred (connect to alt2.gmail-smtp-in.l.google.com[2607:f8b0:4001:c70::1b]:25: Network is unreachable)
10/29/2025, 06:55:34 PM info 1BD0510004A: replace: header Received: from 8136eef12f5b (mailcowdockerized-sogo-mailcow-1.mailcowdockerized_mailcow-network [172.22.1.248])??(Authenticated sender: piyush.a@getcollarup.com)??by mail.getcollarup.com (Postcow) wit from mailcowdockerized-sogo-mailcow-1.mailcowdockerized_mailcow-network[172.22.1.248]; from=piyush.a@getcollarup.com to=piyushdesai204@gmail.com proto=ESMTP helo=<8136eef12f5b>: Received: from [127.0.0.1] (localhost [127.0.0.1]) by localhost (Mailerdaemon) with ESMTPA id 1BD0510004A??for piyushdesai204@gmail.com; Wed, 29 Oct 2025 18:55:34 +0530 (IST)
10/29/2025, 06:50:50 PM info 44C34100219: to=piyushdesai204@gmail.com, relay=none, delay=462, delays=462/0/0/0, dsn=4.4.1, status=deferred (delivery temporarily suspended: connect to alt2.gmail-smtp-in.l.google.com[2607:f8b0:4001:c70::1b]:25: Network is unreachable)
10/29/2025, 06:43:09 PM info 44C34100219: to=piyushdesai204@gmail.com, relay=alt2.gmail-smtp-in.l.google.com[192.178.209.27]:25, delay=1.7, delays=0.88/0/0.8/0, dsn=4.7.4, status=deferred (TLS is required, but was not offered by host alt2.gmail-smtp-in.l.google.com[192.178.209.27])
10/29/2025, 06:43:08 PM info 44C34100219: replace: header Received: from 49d048b20bc7 (mailcowdockerized-sogo-mailcow-1.mailcowdockerized_mailcow-network [172.22.1.248])??(Authenticated sender: piyush.a@getcollarup.com)??by mail.getcollarup.com (Postcow) wit from mailcowdockerized-sogo-mailcow-1.mailcowdockerized_mailcow-network[172.22.1.248]; from=piyush.a@getcollarup.com to=piyushdesai204@gmail.com proto=ESMTP helo=<49d048b20bc7>: Received: from [127.0.0.1] (localhost [127.0.0.1]) by localhost (Mailerdaemon) with ESMTPA id 44C34100219??for piyushdesai204@gmail.com; Wed, 29 Oct 2025 18:43:07 +0530 (IST)

esackbauer

https://docs.mailcow.email/troubleshooting/debug-common_problems/#i-can-receive-but-not-send-mails

https://mxtoolbox.com/SuperTool.aspx?action=dmarc%3agetcollarup.com&run=toolpage
And for Google you must not set DMARC to “none”…

PiyushDesai

esackbauer

what should I added in Dmarc record, would you please suggest?

PiyushDesai

Currently, I’m using Namecheap as my domain provider, which doesn’t support adding TLSA records. Could that be the reason for the issue?

esackbauer

No. It is your DMARC record.

esackbauer

Just do it properly as per documentation. And remove the “2” at the end…
https://docs.mailcow.email/getstarted/prerequisite-dns/#dkim-spf-and-dmarc

PiyushDesai

I have removed 2 from it. and should I keep rest of the record same?

esackbauer

you did not read my first comment or checked what is different from the documentation to your record?

PiyushDesai

sorry, I just don’t understand the document as it is technical doc. but let me understand it and try it on my own. thank you.

Would you please help to confirm?

v=DMARC1; p=reject; rua=mailto:dmarc@getcollarup.com

changed dmarc assistance as below.

The only thing remaining is TLSA. as namecheap domain doesn’t support to add this record it is remaining.

PiyushDesai

After doing it, it giving the same error!

10/29/2025, 08:08:26 PM info 063EA1001F6: replace: header Received: from 0e940598e619 (mailcowdockerized-sogo-mailcow-1.mailcowdockerized_mailcow-network [172.22.1.248])??(Authenticated sender: piyush.a@getcollarup.com)??by mail.getcollarup.com (Postcow) wit from mailcowdockerized-sogo-mailcow-1.mailcowdockerized_mailcow-network[172.22.1.248]; from=piyush.a@getcollarup.com to=piyushdesai204@gmail.com proto=ESMTP helo=<0e940598e619>: Received: from [127.0.0.1] (localhost [127.0.0.1]) by localhost (Mailerdaemon) with ESMTPA id 063EA1001F6??for piyushdesai204@gmail.com; Wed, 29 Oct 2025 20:08:25 +0530 (IST)
10/29/2025, 08:08:27 PM info 063EA1001F6: to=piyushdesai204@gmail.com, relay=alt2.gmail-smtp-in.l.google.com[192.178.209.27]:25, delay=1.5, delays=0.74/0/0.75/0, dsn=4.7.4, status=deferred (TLS is required, but was not offered by host alt2.gmail-smtp-in.l.google.com[192.178.209.27])
10/29/2025, 08:08:14 PM info 1BD0510004A: to=piyushdesai204@gmail.com, relay=none, delay=4360, delays=4360/0.01/0/0, dsn=4.4.1, status=deferred (delivery temporarily suspended: connect to alt2.gmail-smtp-in.l.google.com[2607:f8b0:4001:c70::1b]:25: Network is unreachable)

esackbauer

PiyushDesai After doing it, it giving the same error!

The DMARC record looks correct now, however DNS takes some time to propagate to all DNS servers.
Wait for some hours and try again to send.

PiyushDesai connect to alt2.gmail-smtp-in.l.google.com[2607:f8b0:4001:c70::1b]:25: Network is unreachable

Now this is a different error. Mailcows postfix tries to send the mail via IPv6. It seems your system is not capable or not configured correctly to work with IPv6.
Try do disable IPv6:
https://docs.mailcow.email/post_installation/firststeps-disable_ipv6/

CK_beats

Could it be due to a misconfigured DNS server?
When I query the IPv4 address alt2.gmail-smtp-in.l.google.com I get the public IP 142.250.4.26 back.
The IPv6 address is correct.

Google and Co. now require correct DMARC and SPF records.

Why is TLS encryption rejected? Also atypical.

PiyushDesai

I had disabled IPv6 as per the document but still I am unable to receive the mail.

10/29/2025, 11:15:34 PM info 81515100221: to=piyushdesai204@gmail.com, relay=alt4.gmail-smtp-in.l.google.com[142.250.96.26]:25, delay=15496, delays=15494/0.29/1.5/0, dsn=4.7.4, status=deferred (TLS is required, but was not offered by host alt4.gmail-smtp-in.l.google.com[142.250.96.26])
10/29/2025, 11:30:00 PM info 80F90100252: to=piyushdesai204@gmail.com, relay=alt4.gmail-smtp-in.l.google.com[142.250.96.26]:25, delay=1.8, delays=0.45/0/1.4/0, dsn=4.7.4, status=deferred (TLS is required, but was not offered by host alt4.gmail-smtp-in.l.google.com[142.250.96.26])
10/29/2025, 11:29:58 PM info 80F90100252: replace: header Received: from 6a3b47eba317 (mailcowdockerized-sogo-mailcow-1.mailcowdockerized_mailcow-network [172.22.1.248])??(Authenticated sender: piyush.a@getcollarup.com)??by mail.getcollarup.com (Postcow) wit from mailcowdockerized-sogo-mailcow-1.mailcowdockerized_mailcow-network[172.22.1.248]; from=piyush.a@getcollarup.com to=piyushdesai204@gmail.com proto=ESMTP helo=<6a3b47eba317>: Received: from [127.0.0.1] (localhost [127.0.0.1]) by localhost (Mailerdaemon) with ESMTPA id 80F90100252??for piyushdesai204@gmail.com; Wed, 29 Oct 2025 23:29:58 +0530 (IST)

the above are the logs and below is confirming that only ipv4 is running in mailcow

root@server1:/opt/mailcow-dockerized# docker exec -it mailcowdockerized-postfix-mailcow-1 postconf inet_protocols
/usr/sbin/postconf: warning: /opt/postfix/conf/main.cf, line 202: overriding earlier entry: smtp_address_preference=any
/usr/sbin/postconf: warning: /opt/postfix/conf/main.cf, line 203: overriding earlier entry: inet_protocols=all
inet_protocols = ipv4

esackbauer

Could be MTU size:
https://docs.mailcow.email/getstarted/install/?h=mtu#troubleshooting

PiyushDesai

Is it happening because I have not been able to set TLSA record in namecheap domain as namecheap doesn’t support this record?

esackbauer

no.

maiyannah

I believe the root of this problem is this:

(TLS is required, but was not offered by host alt4.gmail-smtp-in.l.google.com[142.250.96.26])

Now, the real question is why it wasn’t offered, as mentioned above this is atypical.

Check what SSL/TLS ciphers you have enabled, you might now have the ones Google wants and it’s trying to prevent a downgrade attack.

esackbauer

PiyushDesai

Thank you @esackbauer , I applied as per this blog and it solved my problem. Thank you very much sir.

CK_beats

I wouldn’t have thought that!
It is the provider’s fault that Google falls back on unencrypted connections.

maiyannah

CK_beats
If you allow someone to fall back to insecure encryption methods this can allow them to exploit known vulnerabilities in these encryption algorithms. This is called a “Downgrade Attack”

Usually, when a provider is refusing TLS, it is not because they cannot provide TLS, but rather the person that is connecting to them has said in the TLS negotiation they only support algorithms that are insecure (according to the provider anyways). So when this occurs its best to check your TLS settings.