421 CON:B1 The IP address has been temp failed due to a spike in unfavorable e-mail statistics. 421 DNS:NR The Reverse DNS lookup for your IP address is failing. This could be a transient issue. Confirm the IP that sends your mail. Then check the rDNS of that IP using our troubleshooting tools. If it … Continue reading Different Types of AOL SMTP Error Codes. →