If your mail server is sending email and receiving this error try updating your configuration to slow down how fast and how many outbound connections you are making to the internet. You'll also want to check your mail server for abuse, for example, has a host your mail server relays for been compromised and started to send spam?
If others are getting this error message from your mail server or mail filtering appliance you may want to adjust the number of incoming connections and/or rate limiting settings after you have confirmed that the sender is legit and not receiving the error due to abuse.
If others are getting this error message from your mail server or mail filtering appliance you may want to adjust the number of incoming connections and/or rate limiting settings after you have confirmed that the sender is legit and not receiving the error due to abuse.
