HES users with outbound mail scanning enabled intermittently cannot send emails through HES. They receive a Non-Delivery Receipt (NDR) with the SMTP error "421 4.7.0 Error: too many connections".
HES’ relay servers have set limits for the number of connections it will accept:
- smtpd_hard_error_limit = 30
This means that a domain can have a total of 30 simultaneous connections.
- smtpd_client_connection_rate_limit = 10
This means that a domain can make 10 connections every 60 seconds.
- smtpd_soft_error_limit = 25
If HES is to deliver emails to 25 recipient domain names that we do nslookup on, then it starts adding a delay between command lines.
- smtpd_client_connection_count_limit = 30
After 30 nslookup failures, IMHS closes that connection and the domain can immediately make another connection.
To resolve the issue, you need to configure your mail server's outbound mail configuration to conform to these limits. If you need assistance configuring your outbound mail setttings, please contact the appropriate technical support for the mail transfer agent (MTA) you are using.