You can run one of the following processes if you want to stop inbound message processing for a specific domain or IP address, while returning temporary SMTP errors to client hosts. By doing so, messages will not be held on your system. Refer to the 18.1 PART 1. MAPPING TABLES.
To stop inbound processing for a specific host or domain name, add the following access rule to the ORIG_SEND_ACCESS mapping table in the MTA mappings file (typically /msg-svr-base/config/mappings):
ORIG_SEND_ACCESS *|*@sesta.com|*|* $X4.2.1|$NHost$ temporarily$ blocked
By using this process, the sender’s remote MTA will hold messages on their systems, continuing to resend them periodically until you restart inbound processing.
To stop inbound processing for a specific IP address, add the following access rule to the PORT_ACCESS mapping table in the MTA mappings file (typically /msg-svr-base/config/mappings):
PORT_ACCESS TCP|*|25|IP_address_to_block|* $N500$ can't$ connect$ now
When you want to restart inbound processing from the domain or IP address, be sure to remove these rules from the mapping tables and recompile your configuration. In addition, you may want to create unique error messages for each mapping table. Doing so will enable you to determine which mapping table is being used.