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.TH SMTP 8

.SH NAME

smtp, smtpd \-  mail transport

.SH SYNOPSIS

.in +0.5i

.ti -0.5i

.B upas/smtp

[

.B -aAdfiops

] [

.B -b

.I busted-mx

] ... [

.B -g

.I gateway

] [

.B -h

.I host

] [

.B -u

.I user

] [

.BI . domain

]

.I destaddr

.I sender

.I rcpt-list

.in -0.5i

.PP

.in +0.5i

.ti -0.5i

.B upas/smtpd

[

.B -adDfrg

] [

.B -c

.I certfile

] [

.B -h

.I mydom

] [

.B -k

.I evilipaddr

] [

.B -m

.I mailer

] [

.B -n

.I netdir

]

.in -0.5i

.SH DESCRIPTION

.I Smtp

sends the mail message from standard input

to the users

.I rcpt-list

on the host at network address

.I address

using the Simple Mail Transfer Protocol.

The options are:

.TF -

.PD

.TP

.B -a

if the server supports PLAIN or LOGIN authentication,

authenticate to the server using a password from

.IR factotum (4).

See RFCs 3207 and 2554.

This option implies

.BR -s .

.TP

.B -A

autistic server: don't wait for an SMTP greeting banner

but immediately send a

.L NOOP

command to provoke the server into responding.

.TP

.B -b

ignore

.I busted-mx

when trying MX hosts.

May be repeated.

.TP

.B -d

turn on debugging to standard error.

.TP

.B -f

just filter the converted message to standard

output rather than sending it.

.TP

.B -g

makes

.I gateway

the system to pass the message to if

.I smtp

can't find an address nor MX entry for the destination system.

.TP

.B -h

use

.I host

as the local system name;

it may be fully-qualified or not.  If not

specified, it will default to the contents of

.BR /dev/sysname .

.TP

.B -i

under

.BR -a ,

authenticate even if we can't start TLS.

.TP

.B -o

under

.BR -s ,

use TLS even if we don't know the remote system.

.TP

.B -p

ping: just verify that the users named in the

.I rcpt-list

are valid users at

.IR destaddr ;

don't send any mail.

.TP

.B -s

if the server supports the ESMTP extension to use TLS encryption, turn it on for

this session.  See RFC3207 for details.

.TP

.B -u

specify a user name to be used in authentication.  The default name is

the current login id.

.PD

.PP

Finally if

.I .domain

is given, it is appended to the end of any unqualified system names

in the envelope or header.

.

.PP

.I Smtpd

receives a message using the Simple Mail Transfer Protocol.

Standard input and output are the protocol connection.

SMTP authentication by

.I login

and

.I cram-md5

protocols is supported; authenticated connections are permitted to relay.

.PP

The options are:

.TF -

.PD

.TP

.B -a

requires that all clients authenticate to be able to send mail.

.TP

.B -c

specifies a certificate to use for TLS.  Without this

option, the capability to start TLS will not be advertised.

.TP

.B -d

turns on debugging output,

with each connection's output going to a uniquely-named file in

.BR /sys/log/smtpdb .

.TP

.B -D

sleeps for 15 seconds usually at the start of the SMTP dialogue;

this deters some spammers.

Connections from Class A networks frequented by spammers will incur

a longer delay.

.TP

.B -f

prevents relaying from non-trusted networks.

It also tags messages from non-trusted sites when they deliver mail

from an address in a domain we believe we represent.

.TP

.B -g

turns on grey/white list processing.  All mail is rejected (with a

retry code) unless the sender's IP address is on the whitelist,

.BR /mail/grey/whitelist ,

an append only file.

Addresses can be added to the whitelist by the administrator.  However,

the usual way for addresses to be added is by

.I smtpd

itself.

Whenever a message is received and the sender's address isn't on the whitelist,

.I smtpd

first looks for the file

.BI /mail\%/grey\%/tmp\%/\| local\% /\| remote\% /\| recipient\fP,

where

.I local

and

.I remote

are IP addresses of the local and remote systems, respectively.

If it exists and was created more than a few minutes go,

the remote address is added to the whitelist.

If not, the file is created and the mail is rejected with a `try again' code.

The expectation is that spammers will not retry for more than a few minutes

and that others will.

.TP

.B -h

specifies the receiving domain.  If this flag is not specified, the

receiving domain is inferred from the host name.

.TP

.B -k

causes connections from the host at

the IP address,

.IR evilipaddr ,

to be dropped at program startup.  Multiple addresses

can be specified with several

.B -k

options.  This option should be used carefully;

it is intended to lessen the effects of denial of

service attacks or broken mailers which continually

connect.  The connections are not logged and the

remote system is not notified via the protocol.

.TP

.B -m

set the

.I mailer

to which

.I smtpd

passes a received message.

The default is

.BR /bin/upas/send .

.TP

.B -n

specifies the name of the network directory assigned to the incoming connection.

This is used to determine the peer IP address.  If this flag is not

specified, the peer address is determined using standard input.

.TP

.B -p

permits clients to authenticate using protocols which transfer

the password in the clear, e.g.

.I login

protocol. This should only be used if the connection has

previously encrypted using e.g.

.IR tlssrv (8).

.TP

.B -r

turns on forward DNS validation of non-trusted sender address.

.TP

.B -s

causes copies of blocked messages to be saved in a sub-directory of

.BR /mail/queue.dump .

.PP

.I Smtpd

is normally run by a network listener such as

.IR listen (8).

Most of the command line options are more conveniently

specified in the smtpd configuration file stored in

.BR /mail/lib/smtpd.conf .

.SH SOURCE

.TP

.B /sys/src/cmd/upas/smtp

.SH "SEE ALSO"

.IR aliasmail (8),

.IR faces (1),

.IR filter (1),

.IR mail (1),

.IR marshal (1),

.IR mlmgr (1),

.IR nedmail (1),

.IR qer (8),

.IR rewrite (6),

.IR send (8),

.IR tlssrv (8),

.IR upasfs (4)