The prefix for proper is pro
Use the prefix of Mrs. if it is a fomal letter. If not, and you are familiar with them, use their first name.
It is improper.
what is the proper way to address the mayor
The proper prefix for a female if you don't know if she is married is "Ms." This term can be used for all women, regardless of their marital status.
impure
A hyphen is used to separate a prefix from a proper noun or adjective, especially when the combination could be confusing or misleading without it.
The word "improper" contains the prefix "im-" and the root word "proper." The prefix "im-" typically means "not," so "improper" literally means "not proper." The suffix is not present in this word.
Proper
The prefix "im" is a variant of the prefix "in". It creates the opposite of the original word. Examples are: moveable / immovable; possible / impossible.
Ms.
the proper way to address the Queen is by "your majesty" or Ma'm, pronounced like "ham'