I tryed everything to make a Mercury server act as a mail exchanger for another computer and I had no success and I do not believe anymore it is possible with it. This is a last chance I give to this program.
Web Server A runs on V.X.Y.Z on domain dummy.com
Mail server B runs on V.X.Y.W on domain smtp.dummy.com
A have B as MX. Every email sent to email@example.com works ok, but to firstname.lastname@example.org fails in loops.