Today at work, I was searching the web for a semi-reasonable regular expression that I could use to validate email addresses. I say “semi-reasonable” because an RFC 822 compliant regular expression would be quite long. What led to the search was a user with a single-quote (‘) in their address. Damn the Irish.
Anyways, the point of this post is that in looking for a solution, I came across the concept of address tags:
Some mail services allow a user to append a tag to his email address (e.g., joeuser+tag@example.com). The text of tag may be used to apply filtering and to create single-use addresses.