Relay control lets you decide who may use your smtp server (sendmail) to relay messages. Spammers are often borrowing smtp servers to explode a message to a huge list of people. By configuring relay control, you can limit that. Unfortunately, misconfiguring relay control rules may mean that some of your users won't be able to send email.
This checkbox allows you to enable/disable the rules. A new sendmail.cf file is generated, without losing the rules configuration.
Note that this checkbox DOES NOT control the "rejected senders" feature. "Rejected senders" allows you to reject email from well-known spammers. It does not limit the ability to relay.
When relaying using UUCP, the messages are normally queued and delivered at regular interval. You may want to deliver these messages immediately. If you have a low traffic load, this is often necessary. Email is forwarded immediately and users are happy.
UUCP messages may be limited in size. Larger message will be dropped. This is useful for slow modem links. Setting the maximum to 0 will disable this feature (no limit is set).
Enter the name of users for whom you want to defeat the mail host definition. Messages will always be stored locally for those users. This feature is normally used for administrative pseudo users (root for one).
You may want to defeat the "present your system as" field for some users. One such user is root. This easily allows the recipient to determine from which system (which root?) the message originated.
Check this if you intend to use special domain routing. Unfortunately, Linuxconf can't probe the sendmail distribution. You need to know if this sendmail supports a special routing database and which format is supported. These are "compile time" options for sendmail. No sendmail command line option will allow for the retrieval of those compile time features.
Sendmail may use several formats for parts of its database.
It generally defaults to the
dbm format. Please note that
that some sendmails only support one format (dbm). This is
a compile time option.
Different utilities are used to manage email sent to local users. Those utilities provide various extensions allowing the user to tailor the delivery. Procmail, for one, supports fancy filtering. Some people use procmail to split incoming messages into several inboxes based on various criteria.
You can leave this field empty and Linuxconf will locate the proper utility available on your system.
This feature is intended for people without continuous Internet connectivity. This tells sendmail to save the mail without further checking. Later on, one can trigger the delivery of the mail. This is usually done by specifying a post connection command (see Linuxconf ppp dialout support) like "/usr/sbin/sendmail -q". This forces sendmail to process its queue and deliver the messages.
Once in a while sendmail wakes up and tries to deliver email that it was unable to deliver previously. You can see the content of the queue with the command "mailq" (without arguments).
People without continuous Internet connectivity may want to play here. Setting the delay to 0 disable the feature. If your connectivity is on demand, you may want to put a larger number, such as 30 minutes. Then when sendmail will wakes up, it will/should trigger a connection.
Those who disable the feature may want to control sendmail manually (or with a cron job) with the command:
Some mail clients that use SMTP to send email are broken. They generate bad HELO sequences. Sendmail normally rejects such connections. With this option, sendmail is tolerant. It still accepts valid connections.