So, I've just recently set-up a web and mail server, Debian 8 with Apache 2, Dostfix, Dovecot, ISPConfig 3. I used ISPConfig control panel to create mailboxes for my domain, and I am able to send messages without a hassle. Problem is when I try to send to the email address. Gmail and Yandex complains that no such user exist, even when I reply on the message, and Yahoo reports that there's no MX or A records for the domain, even though the records exist. Any pointers on how to go about figuring why this happens?