When sending an e-mail to an aol.com address, I often receive an error message a few minutes later stating:  Error Message 421 DYN:T1  -  "The IP address you are sending from has been temporarily rate limited because it is not whitelisted, unexpected increase in volume, or poor IP reputation."

Is aol.com implying that zoho.com is not Whitelisted or has a poor IP reputation?  This only happens with e-mails to aol.com addresses so I am very suspicious as to AOL's capabilities.

The message goes on to say it will try four more times to re-send to the aol address.  Usually I learn that the addressee did receive the e-mail.