Is it permissible to continue using an email address with the name "Al-Mu'min," knowing that it is one of the Beautiful Names of Allah?

To Allah belong the Most Beautiful Names. Al-Sa'di explained that deviation (ilhad) concerning them occurs by naming someone who does not deserve them, or by negating their meanings and distorting them, or by likening others to them. Accordingly, applying Allah's names to His creation without justification is deviation. As for Allah's names and attributes, they are specific to Him in terms of meaning, but some wordings may coincide with the names of creation. This is only in terms of wording; what is attributed to Allah the Exalted is specific to Him, and what is attributed to a servant is specific to him. Allah has named Himself "The Ever-Living" (Al-Hayy) and "The Giver of Security/The Believer" (Al-Mu'min), and He has named some of His servants with these names. However, this does not imply a sameness of meaning; for both the Creator and the created, there are characteristics and meanings befitting each. Therefore, there is no harm in being named "Al-Mu'min" (The Believer) because this name is not exclusively for Allah, Glorified and Exalted be He, in a way that would prevent creation from being named with it.