Sendmail cf what is dnl

The content of the domain macro is simply generic settings which apply to the domain in question. It is desirable to disable unwanted features as sendmail supports many different types of message transport beyond SMTP and these unused transports can represent unexpected attack vectors for malicious attacks. The more useful FAX service is also supported, however that too is of limited value in a modern world.

This ensures that uncommon transports do not become unexpected attack vectors as the code is old and most likely unmaintained hence it is better to switch it off from the start. The following directives disguise the identity of the software implementation Next, wipe the helpfile, which also gives away the release and version of the software needs to be emptied into a null file The mail server will throw an error if this file does not exist and in that error the software implementation is revealed.

Set the maximum message size in order to limit attachment size. Example below shows a 20M limit Set the level of logging required to elicit sufficient information for audit purposes. Increase verbosity for debugging, but return values to normal levels afterwards to avoid storing un-necessary information. This can be used to over-ride the hostname where the host has an external name or where the TLS certificate on the server uses a common name other than the actual machine hostname. The following privacy flags disable every advertised piece of functionality which is not required for normal mail delivery and enforce some security features.

The following authentication options ensure that authentication amongst other things is not offered unless the administrator wishes to enable it This directly affects the EHLO response and causes less frequently used features to be disabled and therefore not be advertised. The following feature enables access lists for supporting domains other than the local domain names.

Where the identity is the host ip, hostname, netblock, or domain name, and the facility is one of The feature is enabled as follows The content of this file may be.

These users are allowed to spoof their from addresses without root privilege. Sometimes it may be necessary to masquerade as another domain name if the internal DNS namespace is not the same as the external DNS namespace. While masquerading seems a good idea, the genericstable feature enables similar functionality with far greater control over masquerading the source address.

A genericstable data file consists of expression pairs which determine the re-writing of addresses. The following example masquerades host1 and host2 for example. These rules make mail from user1 host1. The following feature will allow aliases which resolve as per the map in order to rewrite lookup requests when considering delivery. Enable selected domains to be routed to a destination of choice, in some cases where [] parenthesis is used over-ride DNS.

The default behavior of sendmail is to deliver by MX despite entries in the mailertable — square parenthesis []are used to note where mailertable over-rides DNS. The square brackets are to over-ride DNS MX record lookup, which sendmail does by default despite there being an entry in the mailertable which would only get attempted if the default MX lookup failed , hence the square brackets instruct sendmail to over-ride DNS MX record lookup.

See my nightmare post on this. The following feature enables the sendmail restricted shell, otherwise known as smrsh, this provides a minimal shell for when sendmail is performing certain commands from the shell. Masquerading is made up of a number of configuration directives. If you receive a lot of E-mail on a regular basis or get hit with sudden floods of it, you may want to explore using the following options:. The first setting instructs Sendmail to have at most 20 processes running at any one time.

These two are useful in preventing a flood of spam from bringing your server to its knees. Hopefully this helps you to better understand Sendmail configuration.

If you find any errors or have any suggestions regarding this please feel free to E-mail me at frank revsys. Quick-Tip: Configuring Sendmail with m4 and the sendmail. After you have made any edits to the sendmail. MTA is a program that moves mail between hosts using a particular network protocol or language.

Sendmail can be easily configured to accommodate new UAs and MTAs, with only minor configuration changes. When a sender wants to send a message, it issues a request to sendmail. The sendmail program operates in two distinct phases:. If there are errors during processing in the second phase, sendmail creates and returns a message. When an error is encountered that can be retried, sendmail places the message in a message queue.

When an unrecoverable error is encountered, automatic routing happens and e-mail is sent to the sender. The sendmail program uses many configuration files.

The sendmail program operates in two distinct phases: In the first phase, It collects messages and stores them as requests from the senders. In the second phase, it delivers the messages to the recipients. Configuration Files The sendmail program uses many configuration files.