I have a mail server in local with a url mail.msd.ci when users type mail.msd.ci they fall on the mikrotik interface instead of falling on the mail server interface.
but outside the local network it works well

Search here on the forum for "hairpin NAT" and check your dst-nat rules. The requests from local users come in via LAN, and chances are high that your dst-nat rules only redirect connections arriving in via WAN. But if you fix that, you'll run into the hairpin connection issue unless the mail server and the local users are in different subnets.

thanks how to correct it
the server and the users are same subnet

OK thanks