Email address specs turn out to be rather complicated.
I really wish people wouldn't code their own checks rather than use already existing standards. Some languages like Java even include proper checks in their standard library: https://java.net/projects/javamail
Several jobs back I had no end of arguments with some Java devs about not writing their own checks, that kept routinely failing on legitimate addresses.
But why do you even need to validate that email? Send the subscriber a confirmation link - if they get it then it was valid, if not then it's on them to fix the situation in whatever way they find fit.
A single massive and unreadable regex isn't an appropriate way to validate a spec that complex. With its complexity it can't be logically evaluated- only tested, whereas a function that breaks the spec out into steps/parts is going to be a lot more maintainable, readable, and auditable.
It really is, I wonder if anyone has tested that extensively. It's so complex that just by reading it I don't think anyone would be able to confirm it matches the RFC correctly.
I really wish people wouldn't code their own checks rather than use already existing standards. Some languages like Java even include proper checks in their standard library: https://java.net/projects/javamail
Several jobs back I had no end of arguments with some Java devs about not writing their own checks, that kept routinely failing on legitimate addresses.