What do you call a person who makes maille?
Solution 1:
The general term "armourer", meaning a smith who specializes in the production of armor, may be used. Alternatively, depending on context, the Middle English term "hauberǧer" from Old French haubergier) more specifically means what you want, which is to say, a maker of maille armours. The former term is far better known, while the latter has long fallen out of use almost entirely, except appearing still as a surname.