Reference: https://www.regular-expressions.info/email.html
I took the last regular expression example that appears at the end of the above web page and made some improvements:
-
I replaced every
‘character (left single quotation mark, code U+2018) with the correct`character (grave accent/backquote/backtick, code U+0060). -
I replaced the last
{1,63}with{2,63}so that the top-level domain must be at least 2 characters long instead of 1.
^(?=[a-z0-9@.!#$%&'*+/=?^_`{|}~-]{6,254}$)(?=[a-z0-9.!#$%&'*+/=?^_`{|}~-]{1,64}@)[a-z0-9!#$%&'*+/=?^_`{|}~-]+(?:\.[a-z0-9!#$%&'*+/=?^_`{|}~-]+)*@(?:(?=[a-z0-9-]{1,63}\.)[a-z0-9](?:[a-z0-9-]*[a-z0-9])?\.)+(?=[a-z0-9-]{2,63}$)[a-z0-9](?:[a-z0-9-]*[a-z0-9])?$
Every single backslash character (\) is replaced with two (\\) to turn the \ escape character itself into a string character.
^(?=[a-z0-9@.!#$%&'*+/=?^_`{|}~-]{6,254}$)(?=[a-z0-9.!#$%&'*+/=?^_`{|}~-]{1,64}@)[a-z0-9!#$%&'*+/=?^_`{|}~-]+(?:\\.[a-z0-9!#$%&'*+/=?^_`{|}~-]+)*@(?:(?=[a-z0-9-]{1,63}\\.)[a-z0-9](?:[a-z0-9-]*[a-z0-9])?\\.)+(?=[a-z0-9-]{2,63}$)[a-z0-9](?:[a-z0-9-]*[a-z0-9])?$