421 Too many concurrent SMTP connections; please try again later.

Question

hi all 
 
 error from direct admin 
 
 w*alak@sejun***.*** R=smart_route T=remote_smtp defer (0): SMTP error from remote mail server after initial connection: host 20*.1**.1*6.7* [20*.1**.1*6.7* ]: 421 Too many 
 concurrent SMTP connections; please try again later. 
 - From the direct admin access can not be sent my host 20*.1**.1*6.7* 
 - Must submit again any time email will be sent - Want to know the cause 
 
 Use UTM 9.4 last version

Vels · Accepted Answer

My log looks like this every day.. 
 Reason ? Well password guessing or spam attacks. 
 I have a lot of connections where the remote end tries to guess or relay with username guessing, others is where they try to single point deliver spam trying to guess executive or administrative email adresses. 
 
 I would not worry about it, but you might want to tweak : Email Protection - SMTP - Advanced - Advanced Settings 
 
 I have recently had to enable country blocking in order to keep my spam and connection attempts down, blocking top 5 spam countries that we never do business with or have users travelling to. 
 So, take this as your mail filter does it job - it takes the punches and dropping the connections.