FIRST, you have to go to…

IPHONE > SETTING > MAIL, CONTACTS, CALENDARS > CLICK ON YOUR ACCOUNT “.…@server.sk”

Then, click on Account > OUTGOING MAIL SERVER SMTP > click on pri­ma­ry smtp serv­er or some­one which is on > you have to set you con­fig­u­ra­tion, like on this picture.

user name and pass, please ask administrator.