The standard (as in most common setup) for djb's qmail, was to accept/forward mail for <prefix>@user.example.com to user@example.com, as in: debian-list@e12e.example.com rather than debian-list+e12e@example.com.
While I believe the + was common for postfix, exim and sendmail?
There even was a spam-fighting scheme that used this - it took a key, and optional date, and a sender address - and generated a unique address you could give out, that was only valid for a certain time, for a certain set of senders.
If the system received a mail with a from address that didn't match the cryptologically signed to-address (e12e-xjjgff65477fc@example.com) - the mail was held back, and the system generated a reply, with a signed reply-to address. A sort of manual grey-listing.
While I believe the + was common for postfix, exim and sendmail?
There even was a spam-fighting scheme that used this - it took a key, and optional date, and a sender address - and generated a unique address you could give out, that was only valid for a certain time, for a certain set of senders.
If the system received a mail with a from address that didn't match the cryptologically signed to-address (e12e-xjjgff65477fc@example.com) - the mail was held back, and the system generated a reply, with a signed reply-to address. A sort of manual grey-listing.