Some mail servers allow users to add tags to the local part of their email address to create unlimited email aliases on-the-fly. For example, if your mail server supports this feature and your email address was:
Then all of the following would be treated as the same email address:
The tag (e.g. "+temp") can be used to apply custom filtering rules. You can also mark an individual tagged address as "invalid" while keeping the main address active. This is helpful for creating single-use or "disposable" email addresses.
SpamHero supports the following delimiter characters for email address tagging:
In other words, SpamHero treats all of the following email addresses as the same address:
Keep in mind that your mail server must support address tagging in order to use this feature. Your mail provider may also refer to this feature as sub-addressing, plus addressing or tagged addressing.
Check out Wikipedia for more information and some of the pitfalls of this feature: