ID #1039

Why should I use an extension address instead of a catchall?

An extension address is a feature of Qmail (and other mail systems) that allows individual users to have as many special purpose email address without any configuration required. Suppose your email address is Say you want to sign up for an account, but you want to treat mail from Amazon specially. If you tell Amazon your email is - you've just created an extension address. No work required.

In contrast, if a catchall was configured to send all mail to, you could tell Amazon your email was simply This is convenient, but there is a disadvantage.

At GeekISP, the mail server is configured to direct extension address to the primary account (i.e. bob-amazon@ goes to bob@, and mary-amazon@ goes to mary@). Furthermore, GeekISP's mail servers are configured to reject mail to invalid recipients during the SMTP conversation. Since catchalls make every possible email address valid, they effectively disable the ability to reject mail sent to invalid recipients during the SMTP conversion, resulting in a lot more spam delivered to the primary account, and more load on the mail servers.

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Last update: 2005-10-16 17:44
Author: Dave Steinberg
Revision: 1.0

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