Linux Server Security, Second Edition

This is the Title of the Book, eMatter Edition

Copyright © 2007 O’Reilly & Associates, Inc. All rights reserved.

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Chapter 9: Securing Internet Email

aliases contains a map of email aliases. Example 9-8 lists part of a sample aliases

list.

As you can see, aliases is fairly self-explanatory: each line starts with an alias (some-

thing we expect to see to the left of the “@” sign in an email address) followed by a

colon and ends with a local username (mailbox name), another alias, or an external

email address. You can map multiple comma-delimited accounts to a single alias to

create mailing lists: this is the case with the last entry in Example 9-8,

mailstooges.

Note that you can “cascade” aliases as in Example 9-8; just be sure not to create any

loops, as in Example 9-9.

On an SMTP gateway, you probably won’t want to do very much with the aliases

database other than to tweak its entries for postmaster, hostmaster, root, and other

infrastructure-related entries. Rather than handling ordinary users’ aliases, a gate-

way should route messages based on destination hostnames and domains (i.e., via

mailertable and virtusers) and leave alias-username translations to the hosts to which

it relays (i.e., the internal mail server, unless for some reason the internal mail server

lacks the ability to do so).

After each edit of aliases, you must convert it to a map file. Unlike with access,

there’s only one