I need your help on my issue very badly.

I have the dovecot version 2.0.9 installed on RHEL linux 6.10 version. It's a single Live server. I need to add a load balancer by adding another server for resilience. 

I cannot upgrade the dovecot version at this time as it is a single live server. If something goes wrong, I will be in trouble.

Basically the requirement/issue is:

a) it's a single live dovecot POP3/IMAP server
b) people are accessing their emails from microsoft outlook (by giving the same server name as IMAP and SMTP server). But more than 100000 emails will be travelled/routed.
c) This server is not rebooted from couple of years.
d) Now they are worried about, just in case if the server is having any issues during the reboot
              or
   if something goes wrong with the server in any case, there will be huge issues.
   
e) They would like to create resilience by adding another server and emails will be travelled from both the servers. If one server is having any issues due to any technical issue and if it doesn't come back easily, then the emails will be travelled through the other server and there will no disturbance to the emails. atleast it travels from the other server.

I have very less knowledge on this. Could you please help me providing the best solution for this.

I will wait for your reply. Please please please help me.

Thanks,
Kishore Potnuru