Second Email Address Setup Problem

I am trying to set up a second email address. I get all of the information
in correctly but a security window pops up & asks for my user name &
password. I input the information but I keep getting the same window pop up.
I cancel out & when I check the second email address it has the user name &
password for the original email address I set up. The pop & smtp are the
same for both email addresses. I contacted our provider & everything I'm
putting in is correct. The main email address is rgroves@xxxxxxxx The
second one I'm trying to set up is mgroves@xxxxxxxx
.