12.1 mtasim interactive mode mode

If you start mtasim without options, you will see the following:

220 mtasim (mailfromd 9.0) ready
(mtasim) _

The first line is an usual RFC 2821 reply. The second one is a prompt, indicating that mtasim is in interactive mode and ready for input. The prompt appears only if the package is compiled with GNU Readline and mtasim determines that its standard input is connected to the terminal. This is called interactive mode and is intended to save the human user some typing by offering line editing and history facilities (see Command Line Editing in GNU Readline Library). If the package is compiled without GNU Readline, you will see:

220 mtasim (mailfromd 9.0) ready
_

where ‘_’ represents the cursor. Whatever the mode, mtasim will wait for further input.

The input is expected to consist of valid SMTP commands and special mtasim statements. The utility will act exactly like a RFC 2821-compliant MTA, except that it will not do actual message delivery or relaying. Try typing HELP to get the list of supported commands. You will see something similar to:

250-mtasim (mailfromd 9.0); supported SMTP commands:
250- EHLO
250- HELO
250- MAIL
250- RCPT
250- DATA
250- HELP
250- QUIT
250- HELP
250  RSET

You can try a simple SMTP session now:

220 mtasim (mailfromd 9.0) ready
(mtasim) ehlo localhost
250-pleased to meet you
250 HELP
(mtasim) mail from: <me@localhost>
250 Sender OK
(mtasim) rcpt to: <him@domain>
250 Recipient OK
(mtasim) data
354 Enter mail, end with `.' on a line by itself
(mtasim) .
250 Mail accepted for delivery
(mtasim) quit
221 Done

Notice, that mtasim does no domain checking, so such thing as ‘rcpt to: <him@domain>’ was eaten without complaints.

So far so good, but what all this has to do with mailfromd? Well, that’s what we are going to explain. To make mtasim consult any milter, use --port (-X) command line option. This option takes a single argument that specifies the milter port to use. The port can be given either in the usual Milter format (See milter port specification, for a short description), or as a full sendmail.cf style X command, in which case it allows to set timeouts as well:

$ mtasim --port=inet:999@localhost
# This is also valid:
$ mtasim --port='mailfrom, S=inet:999@localhost, F=T, T=C:100m;R:180s'

If the milter is actually listening on this port, mtasim will connect to it and you will get the following initial prompt:

220-mtasim (mailfromd 9.0) ready
220 Connected to milter inet://localhost:999
(mtasim)

Notice, that it makes no difference what implementation is listening on that port, it may well be some other filter, not necessarily mailfromd.

However, let’s return to mailfromd. If you do not want to connect to an existing mailfromd instance, but prefer instead to create a new one and run your tests with it (a preferred way, if you already have a stable filter running but wish to test a new script without disturbing it), use --port=auto. This option instructs mtasim to do the following:

1. Create a unique temporary directory in /tmp.
2. Start a new instance of mailfromd. This instance is configured to communicate over a UNIX socket in that temporary directory. Additional arguments and options for the new instance may be given in the command line after a double-dash marker (‘--’).
3. Connect to that filter.

When mtasim exits, it terminates the subsidiary mailfromd process and removes the temporary directory it has created. For example, the following command will start mailfromd -I. -I../mflib test.rc:

$ mtasim -Xauto -- -I. -I../mflib test.rc
220-mtasim (mailfromd 9.0) ready
220 Connected to milter unix:/tmp/mtasim-j6tRLC/socket
(mtasim)

The /tmp/mtasim-j6tRLC directory and any files within it will exist as long as mtasim is running and will be removed when you exit from it.³⁰ You can also instruct the subsidiary mailfromd to use this directory as its state directory (see statedir). This is done by --statedir command line option:

$ mtasim -Xauto --statedir -- -I. -I../mflib test.rc

(notice that --statedir is the mtasim option, therefore it must appear before ‘--’)

You can use an existing directory instead of creating a temporary one. To do so, use the -Xdir:name option, e.g.:

$ mtasim -Xdir:/var/lib/teststate --statedir -- -I. -I../mflib test.rc

Special care should be taken when using mtasim from root account, especially if used with -Xauto and --statedir. The mailfromd utility executed by it will switch to privileges of the user given in its configuration (see Starting and Stopping) and will not be able to create data in its state directory, because the latter was created using ‘root’ as owner. To help in this case, mtasim understands --user and --group command line options, that have the same meaning as for mailfromd.

Now, let’s try HELP command again:

250-mtasim (mailfromd 9.0); supported SMTP commands:
250- EHLO
250- HELO
250- MAIL
250- RCPT
250- DATA
250- HELP
250- QUIT
250- HELP
250- RSET
250-Supported administrative commands:
250- \Dname=value [name=value...]       Define Sendmail macros
250- \Ecode [regex]                     Expect given SMTP reply code
250- \L[name] [name...]                 List macros
250- \Uname [name...]                   Undefine Sendmail macros
250  \Sfamily hostname address [port]   Define sender socket address

While the SMTP commands do not need any clarification, some words about the administrative commands are surely in place. These commands allow to define, undefine and list arbitrary Sendmail macros. Each administrative command consists of a backslash followed by a command letter. Just like SMTP ones, administrative commands are case-insensitive. If a command takes arguments, the first argument must follow the command letter without intervening whitespace. Subsequent arguments can be delimited by arbitrary amount of whitespace.

For example, the \D command defines Sendmail macros:

(mtasim) \Dclient_addr=192.168.10.1 f=sergiusz@localhost i=testmsg
(mtasim) 

Notice that mailfromd does not send any response to the command, except if there was some syntactic error, in which case it will return a ‘502’ response.

Now, you can list all available macros:

(mtasim) \L
220-client_addr=192.168.10.1
220-f=sergiusz@localhost
220 i=testmsg
(mtasim)

or just some of them:

(mtasim) \Lclient_addr
220 client_addr=192.168.10.1
(mtasim)

To undefine a macro, use \U command:

(mtasim) \Ui
(mtasim) \l
220-client_addr=192.168.10.1
220 f=sergiusz@localhost
(mtasim)    

The \S command declare sender socket and host name. These parameters are passed to the connect handler, if one is declared (see connect handler). To give you a chance to use this command, mtasim does not invoke connect handler right after connecting to the milter. Instead it waits until either the \S command or any SMTP command (except ‘HELP’) is given. After calling connect handler the \S is disabled (to reflect it, it also disappears from the HELP output).

The \S command takes 1 to 4 arguments. The first argument supplies the socket family (see Table 4.3). Allowed values are: ‘stdio’, ‘unix’, ‘inet’, ‘inet6’ or numbers from ‘0’ to ‘3’.

The \S stdio (or \S 0) command needs no additional arguments. It indicates that the SMTP connection is obtained from the standard input. It is the default if sender socket is not declared explicitly.

The command \S unix indicates that the connection is accepted from a UNIX socket. It requires two more argument. The first one supplies sender host name and the second one supplies full path name of the socket file. For example:

\S unix localhost /var/run/smtp.sock

The commands \S inet and \S inet6 indicate that the connection came from an ‘INET’ IPv4 or IPv6 socket, correspondingly³¹. They require all four arguments to be specified. The additional arguments are: host name, IP address, and port number, in that order. For example:

\S inet relay.gnu.org.ua 213.130.31.41 34567

or

\S inet6 relay.gnu.org.ua 2001:470:1f0a:1be1::2 34567

Sender socket address can also be configured from the command line (see sender-socket).

Now, let’s try a real-life example. Suppose you wish to test the greylisting functionality of the filter script described in Filter Script Example. To do this, you start mtasim:

$ mtasim -Xauto -- -I. -I../mflib test.rc
220-mtasim (mailfromd 9.0) ready
220 Connected to milter unix:/tmp/mtasim-ak3DEc/socket
(mtasim)

The script in test.rc needs to know client_addr macro, so you supply it to mtasim:

(mtasim) \Dclient_addr=10.10.1.13

Now, you try an SMTP session:

(mtasim) ehlo yahoo.com
250-pleased to meet you
250 HELP
(mtasim) mail from: <gray@yahoo.com>
250 Sender OK
(mtasim) rcpt to: <gray@localhost>
450 4.7.0 You are greylisted for 300 seconds

OK, this shows that the greylisting works. Now quit the session:

(mtasim) quit
221 Done