E-mail alias

All you want to know about E-mail alias

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An e-mail alias is simply a forwarding e-mail address. The term alias expansion is sometimes used to indicate a specific mode of email forwarding, thereby implying a more generic meaning of the term e-mail alias as an address that is forwarded in a simplistic fashion^[1].

1 Usage
2 Control Issue
3 Abuse Issue
4 Notes

Usage

Email aliases can be created on a Mail server. Each e-mail alias simply forwards e-mail messages on to each specified e-mail address. E-Mail aliases are often used to create handy replacements for long or difficult-to-remember e-mail addresses. They can also be used to create generic e-mail addresses such as webmaster@example.com and info@example.com.

On UNIX-like systems, email aliases may be placed into the file /etc/aliases and have the form:

local-alias-name: adifferentlocaluser, anotherlocaluser, an@external.user.example.com

Control Issue

Messages forwarded through an email alias retain the original SMTP envelope sender and recipient. If the message is a blind carbon copy, the recipient can only tell whether the message was forwarded through the alias by examining the message headers. If the recipient forgets the forwarding alias exists, he may ask the sender to stop sending to his actual address, and the sender may not recognize that address.

Abuse Issue

The recipient's SMTP server sees only the forwarding system's IP address. In general it has no reason to trust the Received: headerfield generated by the forwarding system and does not know the originating system's IP address. Therefore, recipients cannot reliably distinguish spam to the alias address from spam generated on the forwarding system. When a recipient reports a message to his ISP as spam, the ISP credits that spam to the forwarding system. ISPs with low abuse threshholds may begin blocking email from the forwarding system.

Notes

^ RFC 2821 defines alias expansion as opposed to the list expansion of mailing lists, noting that the replacement of the address to whom bounce messages are returned makes a key difference.