[theandrewbailey]

Good points. Why do regex tests at all if emails could fail in any number of ways?

If you're going to test for at least 3 characters with a @ in the middle, you probably should implement some other simple rules to have a snowball's chance on the internet:

only one @

no spaces

has TLD (guarantee at least one period after @, and something else after, no consecutive periods)

can't begin or end with a period

[Xylakant]

Your “has TLD” test is already wrong: localpart@tld (example@de) is an odd, but valid address.

[dredmorbius]

A (very simple) regex text might exclude some randomly-entered garbage or inadvertantly invalid address. Even then, the scope and reliability of such tests is minuscule.