Hi John,

Thank you for the reply. Actually it was setup like this by another member, who left the team/company recently. Now it came to me to handle that responsibility. That's how I got in to this. At present I am not able to migrate/upgrade immediately. Because it sends emails around 100K+ emails everyday and I do not want to disturb that.

Coming back to your question, Actually the connection is :

O365/Outlook >> SMTP Gateway Server >> testing.test.com >> 2 POP3 servers.

Actually "testing.test.com", that is FQDN name set in F5 load balancer, where it is having the 2 POP3 servers to route the emails.

When the email was sent from Outlook/O365, first it goes to SMTP Gateway Server. Now the SMTP Gateway server has the postfix rule to send it to "testing.test.com". In this location, I am getting the error in SMTP Gateway Server, where it is not able connect ( lost connection with testing.test.com [xxx.xxx.xxx.xxx] while receiving the initial server greeting).

In SMTP Gateway server, instead of "testing.test.com", if i give the name/ip of any POP3 server, then email delivery is happening successfully to that POP3 server. The above error is coming only when i use the fqdn "testing.test.com", instead of direct POP3 server.

Please let me know if you need any more details. Could you please help me here.

Thanks,

Kishore Potnuru

On Thu, Apr 23, 2020 at 7:13 PM John Stoffel <john@stoffel.org> wrote:

>>>>> "Kishore" == Kishore Potnuru <kishore.reachme@gmail.com> writes:

Kishore> I have the dovecot version 2.0.9 installed on RHEL linux 6.10
Kishore> version. It's a single/standalone Live server.

You should really upgradr your setup.

Kishore> Now I have created another server with the same configuration
Kishore> for the resilince purpose. I also tested and I am able to
Kishore> send the emails to both of the dovecot servers
Kishore> separately/individually. They are working fine.

Dovecot doesn't do the mailing between systems, so i assume you've got
postfix configured? And do you have shared storage behind your two
dovecot instances so that your users don't have to login to multiple
systems to get emails?

Did you read the docs at:

https://doc.dovecot.org/admin_manual/dovecot_cluster_architecture/

Kishore> Now I have added those two servers under a F5 load balancer
Kishore> and created a FQDN (example: testing.test.com). I changed the
Kishore> rules to send the traffic to FQDN "testing.test.com", where
Kishore> it should redirect the email to one of those 2 servers.

So how is your F5 configured to work when one server is down?

Kishore> When I sent the email to FQDN "testing.test.com", I am getting the below error.

Kishore> pf1_inbd/smtp[30292]: 66A5F5F6: to=<xxxxx@yyy.com>,
Kishore> relay=testing.test.com[xxx.xxx.xxx.xxx]:25, delay=13,
Kishore> delays=0.09/0.08/13/0, dsn=4.4.2, status=deferred (lost
Kishore> connection with testing.test.com [xxx.xxx.xxx.xxx] while
Kishore> receiving the initial server greeting)

Kishore> Could you please let me know how to fix this issue? It's a great help for me.

Sounds like you haven't actually setup your system correctly. But
we're not going to be able to help until you provide more details.
It's also not clear from the about log file *which* server gave you
this error.

It would be smarted to start from scratch with an upto date install of
dovecot (and postfix in my opinion) according to the Dovecot docs
above, and test that out in a test environment. Then you would use
'doveadm' sync to migrate user accounts over to the new system.

John