How to set mail delivery settings to use SMTP on another port

Hi, everyone
 
It seems its not possible to define other port different then  25 for SMTP server in Configure Services :: Mail Delivery Settings.

Someone pls confirm and if its not possible can it be added? We have submission port 587 enabled on our mail server, so all users sending out mail have to authenticate via port 587 or 465 SSL, as per RFC4409.
 
I tried hostname:587 and it doesnt work.
 
Thanks,
Flavio