some times me & my staffs getting this msg in return email
failure notice like this:
Hi. This is the qmail-send program at mail.fusionbd.net.
I'm afraid I wasn't able to deliver your message to the following addresses.
This is a permanent error; I've given up. Sorry it didn't work out.
Connected to 184.108.40.206 but sender was rejected.
Remote host said: 501 5.7.1 firstname.lastname@example.org... Sender IP must resolve.
Please any one explain me why I am getting this msg???