problems with mail server setup

Hello folks,
I bought the server app and installed it on my 2009 old macbook pro in order to make it a mail server (and also website server for my web).
I did everything as instructed in manuals, but I didn't managed to connect to the Exchange.
and to be more specific:

1. I created a user and opened mail box (for example, abraham@example.com);
2. I created in DNS section MX with the domain mail.example.com (I also created the same in my domain provider).

when I try to add the email account I created to my iPhone or iMac it's just don't work...
I fill in the email address and the password. after that a dialog box required from me to enter the username (which is the same username I assigned to me in the server app and the password is also the same) and internal URL and external. in both I wrote mail.example.com but it just don't work.

p.s I have static IP.

please help =]

thanks!