Barring users (Domain and web hosting) from receiving mail If you have
Barring users from receiving mail If you have users or automated processes that send mail but will never need to receive it, it is sometimes useful to refuse to accept mail destined for them. This saves wasted disk-space storing mail that will never be read. The blacklist_recipients feature, when used in combination with the access_db feature, allows you to disable the receipt of mail for local users. To enable the feature, you add the following lines to your sendmail.mc file, if they’re not already there: FEATURE(access_db) FEATURE(blacklist_recipients) To disable receipt of mail for a local user, simply add his details into the access database. Usually you would use the ### entry style that would return a meaningful error message to the sender so they know why the mail is not being delivered. This feature applies equally well to users in virtual mail domains, and you must include the virtual mail domain in the access database specification. Some sample /etc/mail/access entries might look like: daemon 550 Daemon does not accept or read mail. flacco 550 Mail for this user has been administratively disabled. grump@dairy.org 550 Mail disabled for this recipient. Configuring Virtual Email Hosting Virtual email hosting provides a host the capability of accepting and delivering mail on behalf of a number of different domains as though it were a number of separate mail hosts. Most commonly, virtual hosting is exploited by Internet Application Providers in combination with virtual web hosting, but it’s simple to configure and you never know when you might be in a position to virtual host a mailing list for your favorite Linux project, so we’ll describe it here. Accepting mail for other domains When sendmail receives an email message, it compares the destination host in the message headers to the local host name. If they match, sendmail accepts the message for local delivery; if they differ, sendmail may decide to accept the message and attempt to forward it on to the final destination (See “The access database” earlier in this chapter for details on how to configure sendmail to accept mail for forwarding). If we wish to configure virtual email hosting, the first thing we need to do is to convince sendmail that it should also accept mail for the domains that we are hosting. Fortunately, this is a very simple thing to do. The sendmailuse_cw_file feature allows us to specify the name of a file where we store domain names for which sendmail accepts mail. To configure the feature, add the feature declaration to your sendmail.mc file: FEATURE(use_cw_file) The default name of the file will be /etc/mail/local-host-names for distributions using the /etc/mail/ configuration directory or /etc/sendmail.cw for those that don’t. Alternatively, you can specify the name and location of the file by overriding the confCW_FILE macro using a variation on: define(`confCW_FILE’,`/etc/virtualnames’) To stick with the default filename, if we wished to offer virtual hosting to the bovine.net, dairy.org, and artist. org domains, we would create a /etc/mail/local-host-names that looks like: bovine.net dairy.org artist.org When this is done, and assuming appropriate DNS records exist that point those domain names to our host, sendmail will accept mail messages for those domains as though they were destined for our real domain name. Forwarding virtual-hosted mail to other destinations The sendmailvirtusertable feature configures support for the virtual user table, where we configure virtual email hosting. The virtual user table maps incoming mail destined for some user@host to some