Ubuntu Postfix refuses SMTP connection after 12th time of successful connecting and sending email

I am sending emails through Postfix which is acting as a relay server - which is working totally fine.

However, I can send maximal 120 emails in 60 seconds. After that I have to wait at least for a minute and then send the next 120 emails.

I have already tried configuring postfix. I am using postfix version 2.11. I have configured the following

smtpd_client_event_limit_exceptions = $mynetworks
anvil_rate_time_unit = 6000s
anvil_status_update_time = 10s

and yes my ip is mentioned in $mynetworks

I have tried to increase the anvil_rate_time_unit which should actually allow more than 12 connections in 1 minute but I still get blocked

I have also tried to configure iptables on the ubuntu server and to configure the firewall settings in plesk: SMTP Ports 25 and 587 and the connection of the ip 1.2.3.4 is always allowed for any incoming, forwarding & outgoing traffic.

But still I am dealing with the issue of only being able to connect to the postfix server 12 times in 1 minute and then wait for 1 minute.

I haven't set any outgoing email limitations in plesk for postfix.

I hope the description is enough to help.

ANY help is appreciated

via Chebli Mohamed