+ as a magic character to effect routing isn't part of the standard. Mail servers are free to route addresses to mailboxes in whatever manner they see fit. That + can appear as a character in an address is part of the standard, just not the behavior of it; a server that treats a+1@ and a+2@ as distinct emails is conforming, and from a sending side, you cannot know if a+1@ and a+2@ will end up in the same mailbox.
(But you're absolutely right that too many sites fail to parse email addresses. Or rather, they over-parse.)
+ as a magic character to effect routing isn't part of the standard. Mail servers are free to route addresses to mailboxes in whatever manner they see fit. That + can appear as a character in an address is part of the standard, just not the behavior of it; a server that treats a+1@ and a+2@ as distinct emails is conforming, and from a sending side, you cannot know if a+1@ and a+2@ will end up in the same mailbox.
(But you're absolutely right that too many sites fail to parse email addresses. Or rather, they over-parse.)