Ham Radio 2000 #1/Ham Radio 2000.iso/ham2000/tcp_ip/ka9q/nos_kit/maildoc3.doc

Text File | 1991-03-15 | 22.7 KB | 661 lines

         NOS mail docs -- G4AMJ/NQ0I and SM0RGV (Rev. 3)

Introduction

Intended audience

These documents are intended for the NOS system operator desiring
to enable the forwarding of mail to other systems. They are NOT
intended as a user guide for the mail capabilities of NOS.

Background

This section of the NOS docs deals with the intricacies of mail
forwarding. You should read and understand this documentation
thoroughly before attempting to forward mail through your NOS box
to the AX.25 BBS world, otherwise you might grossly misconfigure
your system and be the unhappy recipient of flames from BBS
sysops.

This section does NOT deal with the minutae of the mailbox and
its various commands; it assumes that you understand concepts
such as user areas (both public and private) and how to list and
send mail. If you need help with these, please look elsewhere in
the NOS docs.

Apart from the usual domain.txt and other files necessary for
ordinary functionality of NOS, three files are important in the
mail forwarding process. These are : /spool/forward.bbs, /alias
and /spool/rewrite. The contents of these will now be addressed
individually.

/spool/forward.bbs

This file describes the actions taken by NOS in forwarding to
AX.25 BBSes. The file contains a series of forwarding records,
each record being separated by a line containing two or more
hyphens. The template for a forwarding record is:

BBS callsign
Connection route
Connection commands                <zero or more lines>
List of areas to be forwarded      <one per line>
------------                       <end of record>

BBS callsign

This is simply the ordinary call of the remote BBS. A typical
(but not random!) entry might be simply the line:

sm0rgv

The callsign may be followed, on the same line, by a comma
separated list of valid intervals when forwarding is to take
place. Each valid interval is a four digit number: the first two
digits are the beginning hour of the valid interval, the last two
digits are the final hour of the valid interval. For example, if
the first line of a forwarding record looks like:

sm0rgv 0006,1414

then forwarding to sm0rgv will take place only during hours
numbered 00, 01, 02, 03, 04, 05, 06 and 14. Ticks of the mbox
timer outside of these times will not cause mail to be forwarded
to sm0rgv. The default interval for forwarding is 0023.

Connection route

This is the method by which communication is to be established
with the remote BBS. The first token on the line is the type of
protocol to be used. This is one of ax25, netrom or tcp.
Following this is whatever further information the chosen
protocol requires to make the connection. An example connection
route for a simple ax25 connection on interface ax0 is:

ax25 ax0 g3dlh

Connection commands

Connection commands may, optionally, follow the connection route.
These take the form of a full stop (period), followed by the
command which will be transmitted once the connection defined in
the first line of the connection route is established.

For example, suppose that we wish to establish a netrom
connection with sm0rgv-2, through the netrom node #sth67. Then
the connection route and connection command portion of the record
would look like:

netrom #sth67
 .c sm0rgv-2     [ Please note that the full stop would be placed at
                   the beginning of the line; I have placed it here
                   indented by one column simply so that gateways
                   which handle this message do not complain at
                   having a line beginning with a full stop; this
                   convention is followed throughout this documentation]

If the station is reached through digipeating, then the
digipeater callsigns should be in the ax25 route to the
destination callsign. That is, if you wish to forward traffic to
w0ljf, using k2na as a digipeater, then you should have the line:

ax25 route add w0ljf k2na

in your autoexec file.

List of areas to be forwarded

This is a list, one per line, of entries in the /spool/mail
directory which will be forwarded to the remote BBS. An entry of
the form:

callsign

will cause the file /spool/mail/callsign.txt to be scanned for
unread messages. Any such messages are sent to the remote BBS and
deleted from the file.

One can also forward user areas using this mechanism. To do this,
simply place a line containing the name of the area in the
record. So, to forward amsat bulletins to the BBS, one would have
a line:

amsat

This will search the /spool/mail/amsat.txt file; any messages
contained therein which have not been forwarded to the BBS in
question will be forwarded. They will NOT be deleted. The
determining factor as to whether or not entries are deleted is
that if the filename is present in the /spool/areas file, then
there is NO deletion, otherwise there is.

Please note that ONLY FILES IN /spool/mail are checked. In
particular, the outbound SMTP mail queue is NOT checked.

Changing the recipient address

Normally, NOS uses the information in the To: header line to
determine the parameters used by the "S" command during BBS
forwarding. As the To: header is unchanged by all /alias and
/spool/rewrite machinations, the mail will be sent to the BBS
addressed precisely as the originator of the message typed it.
Occasionally, one might want to change this behaviour. In this
case, a line of the form:

area  new_address

in the list of areas to be forwarded will replace the originally
typed destination with the string new_address instead.

/alias

The alias file is used to map LOCAL names to other names, which
may be either local or remote; additionally, from a single input
message, the alias file permits one to produce multiple output
messages. Thus, typical uses for the /alias file are: converting
one local name to another, converting a local name to a remote
name, and exploding a mail message so that it is passed on to
several recipients.

The format of a record in the alias file is very simple:

aliasname       recipient1 recipient2 recipient3
<tab> or <SP>   recipient4 ... recipientN

There is no separation between records in the /alias file other
than a newline.

The aliasname is a local username; that is, it does not contain
an "@" symbol. When the alias file is processed, if the
destination of the message matches precisely the aliasname, then
the mail is redirected to ALL of the alieased recipients.

Scanning of the /alias file is performed by the SMTP server. The
SMTP timer (which controls the SMTP client) is kicked whenever
the mailbox or SMTP server queues something for delivery by SMTP.
Mail transport within a single NOS system is performed through
the SMTP client/server mechanism. The result of these facts is
that as soon as a piece of mail is entered to the mailbox, the
SMTP client is kicked and attempts to deliver the mail (which has
already been scanned by the rewrite mechanism - see below). If
the mail is local to the NOS system (i.e. no "@" sign in the
address), then the /alias file will be scanned and the name
mappings take place.

A few lines in the /alias file might look something like:

bdale   bdale@n3eua
local   fred@k0yum bdale@n3eua [e-mail]
        n5op@n5op jim@k0jtz n0esg@n0esg
g4bki   g4bki@gb7bil._2712.gbr.eu

The system must know how to deliver traffic to each of the
individual addresses in the style in which they are entered in
the /alias file. If the system does not know how to deliver one
of the new addresses, then it will send it to the SMTP gateway
station defined by the 'smtp gateway' command.

Note that it is reasonable, and sometimes desireable, to have
alias records of the form:

area    area dest1 dest2 ...

As the /alias file is scanned only once (see below), this does
not result in an infinite recursion.

/spool/rewrite

The rewrite file is used to perform a one-to-one mapping between
destination addresses as received by NOS and destination
addresses as actually used by NOS. Each record within the rewrite
file comprises a single line, containing either two or three
entries separated by spaces. The first field is the template
field; if a destination address matches the template, it is
replaced by the second field. The third field, which is optional,
is the single letter "r", which, if present, tells NOS to rescan
the rewrite file, using the new destination address to attempt to
match against the templates.

A template may contain asterisks. These stand for a match of any
number of characters (including zero). In the second field, the
character "$", followed by a single digit in the range 1 to 9,
represents the string that matched the respective asterisk in the
template. By way of example, suppose that there is a line in the
rewrite file which looks like:

*@* $1%$[e-mail]

Then, any traffic reaching the system through the mailbox or the
SMTP server, but which is supposed to go to a remote system, will
be redirected to go through g1emm.ampr.org. Suppose that a user
logs on, and sends a message to n0gbe@nq0i. Then the rewrite file
attempts to match "n0gbe@nq0i" against the entry *@*. It matches,
and assignes $1 the value n0gbe, and $2 the value nq0i. The mail
file as written to the disk will no longer be to n0gbe@nq0i, but,
rather, to [e-mail]. [The nomenclature
station1%station2@station3 means the final destination is
station1@station2, and this traffic is to be routed through the
gateway station3.]

As soon as a template match is found, the conversion is performed
and scanning is stopped, unless the third "r" field is present,
in which case scanning restarts from the top of the file.

N.B. It is a good idea to have a line of the form:

*@*.ampr.org $1@$2.ampr.org

at the beginning of your rewrite file. This will cause all
amprnet traffic to be caught early in the rewrite scan, and no
further scanning (and, hence, no unexpected substitutions) will
take place.

Scanning procedure

The two files which are used to determine the disposition of
traffic are scanned under slightly different circumstances. Note
that neither the /alias nor the /spool/rewrite scan makes any
actual changes to the contents of the traffic. In particular, the
To: field remains exactly as it was first entered into the
system.

There are four possible entry routes for traffic into the system:
SMTP, through the mailbox by a user, through the mailbox by a
BBS, and via an external program (like BM) or creation of the
files manually. NOS determines if a piece of traffic was entered
into the system by a BBS by looking for a BBS system ID (like the
"[NET-H$]" block issued by NOS) on the incoming connection prior
to messages being uploaded.

Traffic received by SMTP server

1. The rewrite file is scanned and any changes applied (unless
the traffic was recieved through the local mailbox; in that case,
this step does not occur);
2. If the traffic appears to be local then the alias file is
scanned and any changes or explosions applied.
3. Any copies local to the system are delivered; copies for
remote delivery are placed in the SMTP queue.

Traffic received by mailbox from user

1. The rewrite file is scanned and any changes applied;
2. The traffic is passed to the SMTP client.

Traffic received by mailbox from BBS

1. The rewrite file is scanned and any changes applied;
2. The traffic is passed to the SMTP client.

Traffic entered by external mechanism

1. No scanning occurs;

2. The traffic is passed to the SMTP client.

Headers

Appropriate RFC-822 headers are added to all incoming traffic.
Traffic entering through the mailbox recieves a full complement
of RFC-822 headers; traffic coming through the SMTP server has
only a "Received:" header applied. On forwarding to a BBS, if an
item of traffic contains BBS R: headers, the RFC-822 header is
converted to an appropriate R: line at the time that NOS forwards
the message. (This change only occurs for BBS forwarding;
forwarding by SMTP retains the RFC-822 headers.)

Bulletin Identifiers (BIDs)

The AX.25 BBS system has evolved a reasonably efficient way of
reducing overhead when forwarding bulletins. When a bulletin is
originated on a BBS, it is given a unique bulletin identifier
(BID). This BID should (theoretically) travel with the bulletin,
and should never be changed during the distribution of the
bulletin. Each system keeps track of all received BIDs. If a
forwarding station wishes to forward a bulletin to a BBS, then
the receiving station checks its local list of known BIDs and
informs the transmitting station if it already posesses the
bulletin in question. The NOS mailbox conforms to this protocol.
Received BIDs are stored in the file /spool/history, and are
encoded in the Message-ID: header line of the message by NOS.
Messages forwarded from areas listed in the /areas file will have
their BID (re)generated from the Message-ID: line. Note that ALL
messages from public areas are forwarded with a BID, whether or
not the message was produced with the "SB" command. Like other
BBSes, NOS will inform a transmitting station not to transmit a
bulletin if it is one that NOS already has locally; likewise, it
understands similar messages from other stations to which it
tries to forward.

Note that the BID mechanism is not a part of the SMTP world. If
you are forwarding bulletins through SMTP, there is no mechanism
by which the receiving station can reject the attempted delivery
of a bulletin, even if it already exists on the recipient system.
(Note that a possible workaround is to deliver bulletins to
TCP/IP stations using TCP instead of SMTP. Alternatively, one
could use NNTP, as NNTP commands utilise the Message-ID: line,
from which the BID is derived.) The BID is preserved no matter
which mechanism is used to deliver the bulletin.

Traffic in practice

Now, the big question is, how does one set up these various files
to perform intelligent manipulation of mail? A number of examples
follow. Note that, often, there is more than one way to
accomplish an objective. The following are merely examples (and
not necessarily the most efficient method possible for any given
case). The format used will be:

typed destination -> intended destination

followed by the necessary entries in the alias (/alias), rewrite
(/spool/rewrite) and forwarding (/spool/forward.bbs) files.

Using familiar names - SMTP destination

bdale -> [e-mail]

alias:
bdale   [e-mail]

rewrite:
forward:

Exploding local mail

sysops -> nq0i, [e-mail]

alias:
sysops  nq0i n5op@[e-mail]

rewrite:
forward:

Using familiar names - BBS forwarding

g4bki -> g4bki@gb7bil._2712.gbr.eu, to be forwarded by ai0c

alias:
rewrite:
forward:
ai0c
ax25 ax1 ai0c
g4bki g4bki@gb7bil._2712.gbr.eu
ai0c

Handling incoming bulletins by subject

tcpip@* -> nq0i, tcpip, [e-mail], ai0c@ai0c [a BBS]

alias:
tcpip   nq0i tcpip [e-mail] ai0c

rewrite:
tcpip@* tcpip

forward:
ai0c
ax25 ai0c
ai0c

Let's walk through the above example. An incoming item comes in
addressed to TCPIP@ALLUS. A scan is made through the rewrite
file, and a match is found. The item is redirected to tcpip. The
alias file is scanned; a total of four copies of the item exist
after this, three in local areas tcpip, nq0i and ai0c, and one on
the SMTP queue (for [e-mail]). When the mailbox timer
next ticks, the mail in the local ai0c area will be forwarded on
the ax1 interface to ai0c.

Routing based on Hierarchical addressing

Wyoming -> KE7VS (SMTP)
Nebraska -> AG0N (BBS over the NETROM, NETROM ID WNBBS)
Europe -> W0LJF (BBS over AX.25)

alias:
rewrite:
*.noam            $1.na r
*.us              $1.usa.na r
*.usa             $1.usa.na r

*.ne              $1.ne.usa.na r
*.wy              $1.wy.usa.na r

*@*.*.wy.usa.na   $1%$2.$3.wy.usa.na@ke7vs
*@*.wy.usa.na     $1%$2.wy.usa.na@ke7vs

*.ne.usa.na     ag0n

*.eu            w0ljf

forward:
ag0n
netrom ax0 wnbbs
ag0n
----------
w0ljf
ax25 ax1 w0ljf
w0ljf
----------

Why is the example rewrite file apparently so complicated? This
is to handle poorly constructed hierarchical addresses in a
reasonable way. A full U.S. hierarchical address has the form:
callsign@BBS.#localid.state.usa.na. Many states have no #localid
field. In the example rewrite file above, the first three lines
convert non-standard, but frequently used, U.S. designators to
the more standard format. It is common for users not to use a
full hierarchical address if the destination is relatively local.
For eample, a user might easily use only .wy instead of the full
.wy.usa.na if he is geographically close to Wyoming. The second
grouping of two lines handles this problem. Note the third, "r",
field in all the entries so far.

The remainder of the file handles properly formatted hierarchical
addresses. The two Wyoming entries handle the cases with and
without a #localid field. Differentiation between these cases is
not necessary for BBS forwarding.

General bulletin handling

The details of bulletin handling will vary somewhat from place to
place, as there are several distinct styles of bulletin handling
currently in use in the AX.25 BBS world. In general, it is
necessary to arrange one's system so that it accepts bulletins
from BBSes, forwards them to one or more stations, and also
handles intelligently bulletins input by users into NOS.

Suppose that we sish to handle bulletins @JUNK. We are to deposit
them locally in the junk area, and also forward to BBS g4bki. We
also know that we generally receive @JUNK bulletins from g4amj, a
local BBS which handles much bulletin traffic.


alias:
rewrite:
*@junk   junk

forward:
g4bki
ax25 ax1 g4bki
g4bki
junk
----------
g4amj
ax25 ax1 g4amj
g4amj
junk
----------

All incoming @JUNK traffic is written to the junk area (which
should be an explicit entry in the /spool/areas file). Each tick
of the mailbox timer, NOS scans the junk area for traffic not
forwarded to g4bki or g4amj and attempts to deliver unforwarded
bulletins. Usually, g4amj will respond with a "Have it" message
and the bulletin will not be forwarded. Any bulletins @JUNK
deposited locally by users will automatically be sent to both
g4bki and g4amj.

Questions and Answers

Q. Under what circumstances does NOS request reverse forwarding
from a BBS?

A. NOS requests a reverse forward after completing any forwards
of its own to the BBS. If no traffic was queued for a given BBS,
then no connection is attempted, so no reverse forward request is
issued.


Q. What kinds of message types does the NOS mbox support?

A. Basically, NOS supports all two letter commands starting with
an "S". If the mailbox has not received an SID banner (the
"[NET-H$]") from a connected station, then an SF command will
send a followup to the address specified on the command line. The
SR command will send a reply to the current message. One can also
issue the command "SR <number>", where <number> is the number of
the message to which you want to generate a reply. All other
variations cause an X-BBS-Msg-Type: header to be added to the
message. When a message with such a line is forwarded to a BBS,
it is sent to the BBS with the appropriate message type as the
second letter in the "S" command to the BBS.

If NOS has received a valid SID, then ALL S commands are handled
by the X-BBS-Msg-Type: mechanism outlined above.




































































Logic map of the mailbox

============== AX.25 === NET/ROM === Ethernet === Loopback =================
       |                   |                   |                   |
       |                   |                   |                   |
+--------------+    +--------------+    +--------------+    +--------------+
|              |    |              |    |              |    |              |
|   Mailbox    |    | SMTP client  |    | SMTP server  |    | BBS Forward  |
|              |    |              |    |              |    |              |
+--------------+    +--------------+    +--------------+    +--------------+
       |                   ^                   |                   ^
       |                   |                   |                   |
       v                   |                   v                   |
+--------------+    +--------------+    +--------------+    +--------------+
|              |    |              |    |              |    |              |
| Add RFC822   |    | Use MX or A  |    | Add Received |    | Add own R:   |
| header suite |    | type records |    | line         |  +>| line         |
|              |    |              |    |              |  | |              |
+--------------+    +--------------+    +--------------+  | +--------------+
       |                   ^                   |          |        ^
       |                   |                   |          |        |
       v                   |                   v          |        |
+--------------+    +--------------+    +--------------+  | +--------------+
|              |    |              |    |              |  | |              |
| Get Rewrite  |    | Use optional |    | Apply Rewrite|  | | Strip RFC822 |
| file address |    | SMTP gateway |    | file address |  | | header suite |
|              |    |              |    |              |  | |              |
+--------------+    +--------------+    +--------------+  | +--------------+
       |                   ^                   |          |        ^
       |                   |                   |          |        | Yes
       v                   |                   v          |        |
+--------------+           |            +--------------+  | +--------------+
|              |   No      |            |              |  | |              |
| Local addr?  |-------+   |            | Alias file   |  +-| Any R: lines?|
|              |       |   |            |              | No |              |
+--------------+       |   |            +--------------+    +--------------+
       |               |   |                |  |  |                ^
       | Yes           |   |                |  |  |                |
       v               |   |                v  v  v                |
+--------------+       v   |            +--------------+    +--------------+
|              |    +--------------+    |              |    |              |
| Apply Rewrite|    |              | No | Local        |Yes | /spool/mail/ |
| file address |--->| SMTP queue   |<---| address?     |--->| directory    |
|              |    |              |    |              |    |              |
+--------------+    +--------------+    +--------------+    +--------------+