Definitely.
I didn't take the time to battle test it, but when I read (\.[^<>()\[\]\\.,;:\s@"]+)*) in the sample above, I started to smell redos opportunities here
The page regex101.com is really useful for analyzing regular expressions.
Note that /^[a-zA-Z]+$/ misses a lot of letters, like "é" or "字"
Jason Knight
The less code you use, the less there is to break
Except for lengths. :D