I understand that the first email regex is simplified and as a result doesn't handle oddities such as weird symbols, quotations and IP addresses, but it should be able to handle modern TLDs. Not only do you have names longer than 4 characters, but internationalised domain names starting with --.

https://en.wikipedia.org/wiki/List_of_Internet_top-level_dom...

Depending how simple you want it either:

\b[A-Z0–9._%+-]+@[A-Z0–9.-]+\.(xn--[A-Z0-9]|[A-Z]+)\b

or simpler:

\b[A-Z0–9._%+-]+@[A-Z0–9.-]+\.[A-Z0-9-]+\b

However you could argue that validating email via regex misses the point entirely. A simple, permissive regex is all you really need assuming you are actually sending an email to check that the account exists.