Postfix & Dovecot error The maximum number of concurrent server connections has exceeded a per-source limit

EmailServer : 672 : Error Sending E-mail [Smtp Error : [4.3.2 The maximum number of concurrent server connections has exceeded a per-source limit, closing transmission channel

First I checked the current config:

 # dovecot -a |grep mail_max_userip_connections 
 mail_max_userip_connections = 10

Which is 10 as default.

This parameter shows up in 3 files:

 /etc/dovecot/conf.d/20-imap.conf:  #mail_max_userip_connections = 10 
 /etc/dovecot/conf.d/20-managesieve.conf:  #mail_max_userip_connections = 10 
 /etc/dovecot/conf.d/20-pop3.conf:  #mail_max_userip_connections = 10

I uncommon them and changed 10 to 20, restart the service

 /etc/dovecot/conf.d/20-imap.conf:  mail_max_userip_connections = 20 
 /etc/dovecot/conf.d/20-managesieve.conf:  mail_max_userip_connections = 20 
 /etc/dovecot/conf.d/20-pop3.conf:  mail_max_userip_connections = 20

 service dovecot restart

Double check when the service is back online:

  # dovecot -a |grep mail_max_userip_connections 
  mail_max_userip_connections = 20 
  mail_max_userip_connections = 20 
  mail_max_userip_connections = 20