regex - Regular Expression for email to check repetitive characters -

i'm validating email address regular expression. test following conditions:

minimum of 3 characters in name, symbol @, minimum 3 characters in first part of domain, dot,no more 3 repetitive characters

i tried regular expression , it's working fine cases except last one.

/^[a-za-z0-9._%+-]{3,}\@[a-za-z0-9.-]{3,}\.[a-za-z]{2,4}$/

it's not checking repetitive character(any character) after dot(.)

not ok: test@test.ccccom, test@test.coooom

ok : test@test.com

don't know wrong last portion of re.

any input appreciated.

you can use following regex:

^(?!.*([a-za-z0-9])\1{3})[a-za-z0-9._%+-]{3,}\@[a-za-z0-9-]{3,}\.[a-za-z]{2,4}$

changes made:

(?!.*([a-za-z0-9])\1{3}) - negative lookahead makes sure none of characters repeat more thrice in row.

the rest of regex same is, except removal of . second character class.

if want disallow repeated characters after last ., use following instead:

^[a-za-z0-9._%+-]{3,}\@[a-za-z0-9-]{3,}\.(?!([a-za-z0-9])\1{3})[a-za-z]{2,4}$

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