In what sense do you think this isn’t following the email standard? The plus sign is a valid character in the local part, and the standard doesn’t say how it should be interpreted (it could be a significant part of the name; it’s not proper to strip it out) or preclude multiple addresses from delivering to the same mailbox.

Unfortunately the feature is too well-known, and the mapping from the tagged address to the plain address is too transparent. Spammers will just remove the label. You need either a custom domain so you can use a different separator (‘+’ is the default but you can generally choose something else for your own server) or a way to generate random, opaque temporary addresses.

If you want to talk about non-compliant address handing, aside from not accepting valid addresses, the one that always bothers me is sites that capitalize or lowercase the local part of the address. Domain names are not case-sensitive, but the local part is. Changing the case could result in non-delivery or delivery to the wrong mailbox. Most servers are case-insensitive but senders shouldn’t assume that is always true.

CVS and E*Trade both refused to accept my fairly standard user@mydomain.info address during initial registration, but had no issue changing to that address once the account was created. It would be nice if their internal teams communicated a bit better.

The full email address syntax described in the RFC cannot be precisely matched with a mere regular expression due to the support for nested comments. The need to track arbitrarily deep nesting state makes it a non-regular language.

If you remove the comments first the remainder can be parsed with a very complex regex, but it will be about a kilobyte long.

Your intake of sugar participation in extreme sports absolutely impacts other people when you end up with chronic health issues that other people have to help pay for.

It’s not as if there’s some natural law obligating you to pay for anyone else’s health issues. Your government is responsible for externalizing that private cost onto you and others, effectively subsidizing risk-taking and irresponsibility. If you don’t like it, insist that people pay for their own health care and insurance at market rates, without subsidies.