- https://en.wikipedia.org/wiki/Email_address#Sub-addressing
- https://www.cs.rutgers.edu/~watrous/plus-signs-in-email-addresses.html
- https://security.stackexchange.com/questions/65244/what-are-the-security-reasons-for-disallowing-the-plus-sign-in-email-addresses
- http://www.catb.org/jargon – plussing does not get mentioned in the Jargon File
- https://support.google.com/mail/answer/22370?ctx=gsidentifer#zippy=%2Cfilter-using-your-gmail-alias
e-mail messages addressing John.Doe+MailingListName@gmail.com are meant to actually go to johndoe@gmail.com, in other words:
- “.” characters actually get removed for computing the real mail box
- everything starting the “+” character and going to the “@” character (not including the latter) gets removed entirely
On the recipient side, software can check on plussing and may come to decisions based on the string between the “+” and the “@”.
Yes, gmail and hotmail and posteo do support plussing. GMX does not support plussing.
On my domains I have a catch-all rule for e-mail forwarding aliases, and procmail rules help me with the checks.
When I will get around to it, I will write here under “e-mail”, how I make use of IMAP, procmail, and fetchmail.
Update 2023-04-04: There is another variant of sub-addressing: if you own the full right side of the “@”, you can also use the full left side of the “@” as a “catch all”, i.e. mail_jh@John.Doe.name and mail_aw@John.Doe.name can be John Doe’s dedicated mail address for me (Jochen Hayek) resp. “aw” (like Alex Winner).