Just a base level regex before sending emails, to avoid some errors sending to non-email addresses and logging otherwise unnecessary errors.
I have a .blue email address and it's amazing how many sites still won't accept it. I keep a spare Gmail account for these.
I keep a Gmail for the same reason.
I tried to add a .wiki link to a Reddit profile recently and their filters also say that domain is invalid.
That's absurd, there's a .wiki that's almost definitely in the top 20 most visited websites in Korea, if not higher.
People accidentally typing their name in the email field, stuff like that. I've done that.
The problems with your .blue is obviously completely unrelated to the "email.contains('@')" check the poster is doing.
You can do quite well at this, if you're willing to not restrict yourself to regexes and commit to some amount of hackery. One system I worked on used a simple regex (just what is described here IIRC - assert the existence of an @ sign), plus did an MX check on the domain, plus warned (not errored) if the domain was within 1 or 2 Levenshtein distance of any of a list of most common email domains (yahoo, gmail, etc). Statistically it seems like we saved people a lot of grief with this simple filtering.
myemail+90sdev@gmail.com
Possibly these validators are working exactly as intended and don't want you to know which service sold your email to spammers.
Then again maybe spammers are smart enough to strip of the + from email lists they purchase.
Most of the time they're too disinterested to notice. Oil change places always notice for some reason.
I'll look through my spam foldsr tomorrow and see who's been naughty.
Documented as "subadressing" in RFC 5233, and the default for both sendmail and postfix, amongst others. As such, often 'accidentially' supported by many mail providers even when undocumented. Google didn't introduce them, nor are they 'unconventional'.