SMG classifies IP's in “Connection Classification” it need to be received. When SMG receive a large number of connections of many IP addresses, SMG stay with very slow performance and delay too long to send and receive e-mails.
Check the ”IP Reputation Lookup“
To check ”IP Reputation Lookup“ Go to (Reputation > IP Reputation Lookup)
Type IP Address in “Enter an IP address to query for:” and click in “Find”
Enable some filters in SMG to reject connections (It will allow the connection to be blocked behind of pass by SMG and the performance will not be affected).
WARNING: Before of enable any filters please check some considerations in your environment and how much it will impact it.