You can allow specific client to bypass the
This would first take the specified action in
client_access, and if it doesnt match any rule listed there, then reject the senders that have no valid domain.
The syntax in client_access would be:
Once this file is setup, execute the following command to generate the indexed version of this file (db):
Reload postfix and you should be ok.
More doc on access tables
More on smtpd_client_restrictions
If for some reason you need to debug this, you could try to enable debugging in smtpd depending on who is connecting to your service. Edit
/etc/postfix/master.cf, locate smtpd service and add a line like this one:
smtp inet n - - - - smtpd
-o debug_peer_level=10 -o debug_peer_list=126.96.36.199
It will enable debug only for peer 188.8.131.52. This should give you an idea of what is happening when the client 184.108.40.206 is connecting to the smtp service to send you email, by looking at your mail log.