Data Masking Emails using Formulae

It appears someone gave you a formula that does work but I cleaned up your version and theirs and made both dynamic arrays so they apply to the whole column at once:

I think this is a variation on your original using REPLACE:

=REPLACE(E2:.E99999,2,FIND("@",E2:.E99999)-3,REPT("*",FIND("@",E2:.E99999)-3))

and a multi-segmented version:

=LEFT(E2:.E99999,1) & REPT("*",FIND("@",E2:.E99999)-3) & MID(E2:.E99999,FIND("@",E2:.E99999)-1,LEN(E2:.E99999))

and you could further refine them using LET.  For example:

=LET(n,FIND("@",E2:.E99999)-3, REPLACE(E2:.E99999,2,n,REPT("*",n)))