Internet email rejected

In an attempt to setup a personal webmail server on my current Debian Buster machine I have installed postfix and dovecot and tested as well as I am able from withing my network and all is well. I can send and receive email from and to any of the machines on my Intranet but.....
I cannot receive emails from the Internet.
I have checked port settings on the router and it appears all well
Please advise what I may have got wrong.