SMTP Error Codes

When Deep Discovery Email Inspector blocks an email message based on Sender Filtering settings, Deep Discovery Email Inspector sends the following SMTP error codes to the upstream MTA.

Note:

Make sure that the upstream MTA can take the necessary pre-configured actions upon receiving these error codes. For example, creating an event log or sending notifications to senders.

Table 1.

Blocking Feature

SMTP Error Code

Message

Sender Filtering/Authentication settings (DHA Protection, Bounce Attack Protection, SMTP Traffic Throttling, SPF, DKIM, DMARC)

421

Block temporarily (Sender Filtering/Authentication)

521

Block permanently (Sender Filtering/Authentication)

Email Reputation Service

450

Temporary denial of connection (450) for Zombie matches (ERS)

550

Permanent denial of connection (550) for RBL+ matches (ERS)