Regular expression to mask email except the three characters before the domain

I am trying to mask email address in the following different ways.

1. Mask all characters except first three and the ones follows the @ symbol. This expression works fine.

   (?<=.{3}).(?=[^@]*?@)

   [e-mail] -> abc*****@gmail.com

2. Mask all characters except last three before @ symbol.

   Example : [e-mail] -> *****[e-mail]

   I am not sure how to check for @ and do reverse match.

Can someone throw pointers on this?

Answer

Maybe you could do a positive lookahead:

.(?=.*...@)

See the online Demo

• . – Any character other than newline.
• (?=.*...@) – Positive lookahead for zero or more characters other than newline followed by three characters other than newline and @.