Just about everything you do online asks you for your email address. You may also exchange email addresses with others in various contexts for various reasons. While this is a really convenient way to stay connected, it can be hard to figure out the context in which each person or organization sending you email originally got your address. This is where the idea of tagging your email address comes into play.
A tag is a short label you attach to your email address to identify or categorize it. By assigning a tag, you’re able to better identify and organize your incoming email. Tags also make it possible for you to track where inbound junk mail is coming from.
The tag itself has no effect on how email sent to that address is routed; the email server will deliver email addressed to user+tag@w3ctag.org as though it were addressed to user@w3ctag.org. The tag portion of the email address can then be used both for filing email and for screening it. it’s just extra information that your email server ignores.
If you register at a website with your email address plus one or more tags:
username+sitename+yyyy-mm-dd@w3ctag.org
^^^^^^^^ ^^^^^^^^^^
tag1 tag2
…then if you ever receive unsolicited email to this address, it’s not only easy to track where the sender got your address from, but also to block this address for future emails.
The format of email addresses is local-part@domain. The following constraints are specific to the local-part portion (i.e., everything before the ‘@’ symbol):
must not exceed 64 characters in length
john+shenyang-hotel-management-limited-company-meeting-2019-10-23@domain
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
65 characters exceeds the maximum limit of 64 characters for the local-part
should contain only letters A-Z and a-z, digits 0-9, plus (+), hyphen (-), underscore (_), and dot (.)1
john+björk-fan-site@domain
^
Non-ASCII characters may not be accepted by some sites
Non-ASCII characters may not be handled properly by some email servers
john+yahoo!@domain
^
Special characters may not be accepted by some sites
Special characters may not be handled properly by some email servers
must not begin or end with a dot (.), and must not contain consecutive dots
john+tag.@domain
^
Local-part must not end with a dot
john+ready...set...go@domain
^^^ ^^^
Local-part must not contain consecutive dots
Technically, the list of valid characters is actually more extensive, but not all sites or email servers adhere to the standard. To avoid compatibility issues, we recommend you limit yourself to just the characters listed. ↩︎