Thats possible. Here an example of a open source mail server: https://github.com/mailcow/mailcow-dockerized/blob/f5522a809cd03ceb0d6e05fac337a2c5a7380167/data/c

Thats possible. Here an example of a open source mail server: https://github.com/mailcow/mailcow-dockerized/blob/f5522a809cd03ceb0d6e05fac337a2c5a7380167/data/conf/rspamd/custom/fishy_tlds.map#L43 https://github.com/mailcow/mailcow-dockerized/blob/f5522a809... They consider some TLDs as "fishy".