Recommendation letter from an Emeritus Professor
No, the form of the email address won't matter. You want letters from those who can best support your candidacy, so don't bother with others. If they are the best choice to support you, then get the letter from them. Someone with emeritus status has had a long career and is probably well known. 

Of course, a former professor should identify them self as such in the letter, naming the institution. 

I doubt that electronic systems will block you, as not all letters come from academics in any case. 

Some of us still maintain university hosted web sites and are listed among emeritus faculty.