Sub-addressing A number of email systems support
sub-addressing, also known as "plus" or "tagged" addressing, where a tag can be appended to the local portion of an email address (the part to the left of the "@") but with the modified address being an alias to the unmodified address. For example, the address joeuser+tag@example.com denotes the same delivery address as joeuser@example.com. The text of the tag may be used to apply filtering, or to create single-use addresses. If available, this feature can allow users to create their own disposable addresses. However, this system reveals the user's delivery address to email recipients.
Multiple email aliases Another approach is to register multiple auxiliary email addresses as
aliases which forward all mail to one main address. The advantage of this approach is that the user can easily detect which auxiliary email is receiving spam and block or dispose of it. Some services require additional time to set up forwarding, but others allow the spontaneous creation of new addresses without having to register them with the service in advance. Although this method allows storage and access of all emails from a single account, some services require separate passwords for each alias.
Wildcards Another method is to use a catch-all address and forward mail to the real mailbox using
wildcards. Many mail servers allow the use of an asterisk (*), meaning "any number of characters". This makes the whitelist automatic and only requires the administrator to update the blacklist occasionally. In effect, the user has one address, but it contains wild-cards,
e.g., "me.*@my.domain", which will match any incoming address that starts with "me." and ends with "@my.domain." This is very similar to the "+" notation, but it may be even less obvious since the address appears to be completely normal. == Concerns ==