Fwd: Load balancer for dovecot servers - Not able to send emails

[John Stoffel]

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

Dovecot doesn't do *any* mailing, that's handled by postfix or
sendmail or qmail.  I think postfix is the best.  You can run your
outgoing email on a seperate server without any problems.

Kishore> Coming back to your question, Actually the connection is : 

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

Why are you running POP3 in this day and age?  Wait, don't answer
that.  :-)

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

By POP3, I assume you mean the two dovecot servers?

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

What is the gateway server and how is it configured to deliver the
mail to the backend servers?  

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

This is because your two backend servers probably don't know how to
accept email for the testing.test.com domain IP/name.  Again, this
sounds like a mailing problem, not a dovecot problem.  

You need to provide lots of details here.  And ideally the logs from
both the SMTP gateway, and the two backend servers, along with full
details of how they are configured.

But from what I see here, this is a mail configuration problem, not a
dovecot issue.  But you don't give enough details.  


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



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

>>>>>> "Kishore" == Kishore Potnuru <kishore.reachme at 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. 
   
Kishore>     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.
   
Kishore>     Dovecot doesn't do the mailing between systems, so i assume you've got
Kishore>     postfix configured?  And do you have shared storage behind your two
Kishore>     dovecot instances so that your users don't have to login to multiple
Kishore>     systems to get emails?
   
Kishore>     Did you read the docs at:
   
Kishore>       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.
   
Kishore>     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 at 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.
   
Kishore>     Sounds like you haven't actually setup your system correctly.  But
Kishore>     we're not going to be able to help until you provide more details.
Kishore>     It's also not clear from the about log file *which* server gave you
Kishore>     this error.
   
Kishore>     It would be smarted to start from scratch with an upto date install of
Kishore>     dovecot (and postfix in my opinion) according to the Dovecot docs
Kishore>     above, and test that out in a test environment.  Then you would use
Kishore>     'doveadm' sync to migrate user accounts over to the new system.
   
Kishore>     John