Almost all E-Mail validation algorithms are wrong
Almost all E-Mail validation algorithms on the web are wrong. And why are they too strict?
Because the RFC allows way more characters but allows hosters to restrict their own mail addresses more ofc.
And most hosters will go for alpha-numeric with the most basic special characters like underline and minus.
With a de-facto standard of all mail hosters going a restricted way, it seems people implementing email addresses validation algorithms will not check the RFC.
And write way too strict checkers.
With quotation or escaping even another @ is allowed in your mail address.
Although not very readable and very uncommon this allows for further hierarchical email addresses on one host for example.
How long is your regexp?
Valid [via]:
!def!xyz%abc@example.com"Abc\@def"@example.comcustomer/department=shipping@example.com