Email validation not working correctly

[BigWhale]

When creating new users with wp_insert_user or when changing user's email address in UI. Emails such as 'joe@com' or 'jill@sometld' are not accepted as valid email addresses.

Those email addresses are rarely used, but they are valid email addresses.

[SergeyBiryukov]

Related: #17433, #17491, #21730, #25108.

[BigWhale]

So many related bugs. I'd suggest that validation includes only validating if '@' character is present, the absence of trailing dot, and the absence of double dots. Everything the else is a fair game.