[CTX] [ALL] SMTP proxy/server

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SMTP proxy/server

Example: proxy SMTP-DeleGate

// with aliasing and filtering


firewall# delegated -P25 SERVER=smtp://mail-server/ \


MOUNT="foo@bar smtp://foo2@bar2" \
MOUNT="* smtp://-"

SMTPCONF parameter* ==  SMTPCONF=what:conf
                    --  default: SMTPCONF=bgdatasize:64K

myname:name

Specify the name of this host to be shown to client or server in its opening message, HELO command, and so on.

reject:{nohelo,nofrom,pipeline,nomx,notselfmx,notmxhelo}

Reject the DATA or the session if a specified condition is true.

"nohelo" -- the client does not say "HELO"

"nofrom" -- the client does not say "MAIL FROM"

"pipeline" -- the client send command without waiting server's response

"nomx" -- the client's host does not have a MX record

"notselfmx" -- the client's host is not the MX of itself

"notmxhelo" -- the domain in the HELO is not the MX of the client's host

Multiple conditions can be specified concatenated with "+" as SMTPCONF="reject:nomx+nohelo+nofrom+pipeline".

bgdatasize:N

If the data is larger than N bytes, relay it in background. This means relaying a "DATA" command to a server without having a client wait for the response for "QUIT" command from the server. Note that only one mail DATA can be relayed in background and the mail can be lost if the DeleGate crashes before finishing the forwarding because the current DeleGate have no mechanism for spooling and retransmission.

maxrcpt:N

Limit the acceptable maximum number of recipients (by RCPT commands)

MX:server[:domain]

Specify the SMTP server toward which mails (bound for the domain) are forwarded. The server can be specified based on the destination address of the E-mail to be relayed (it is the address indicated in the RCPT command on the SMTP protocol). The character "*" in server is replaced with the domain part of a E-mail address as "foo@domain". The prefix "-MX." to a domain name as "-MX.domain" represents the mail-exchange server of the domain (which is retrieved by DNS as the MX record of the domain or host).
The default specification is SMTPCONF="MX:{-MX.*,*}" which means trying the MX first, and if it failed, then try direct connection to the domain as a hostname.

Examples:
SMTPCONF="MX:smtpserver" -- use the smtpserver as the upstream SMTP server
SMTPCONF="MX:{smtpserver1,smtpserver2}" -- try the SMTP servers in the order
SMTPCONF="MX:{-MX.*,*}" -- the default configuration
SMTPCONF="MX:{-MX.*,*,smtpserver}" -- adding a backup SMTP server
SMTPCONF="MX:{*,-MX.*}:*.localdomain" -- forward directly to the host if it's in localdomain
SMTPCONF="MX:smtpserver:{*.dom1,*dom2}" -- a server for the specified domains


callback[:[T][:srcHostList]]

Callback to the SMTP server on the client host which is making current request (on HELO command). If there is not a SMTP server on the client host, then the processing of the request will be delayed up to T seconds. This could be effective to reduce DDoS type SPAM messages which are relayed exploiting non-SMTP servers. SMTPCONF="callback" is the abbreviation of SMTPCONF="callback:20:*".

bcc:emailAddr[:srcHostList]

Append the emailAddr to the list of recipients.

SMTPGATE parameter  ==  SMTPGATE=dirPath
                    --  default: SMTPGATE='${ETCDIR}/smtpgate'

Specify the configuration directory for SMTPGATE, a SMTP to {SMTP,NNTP} gateway. To accept and relay SMTP messages bound to "recipient@the-host-of-DeleGate", create a configuration directory at "SMTPGATE/users/recipient" for each recipient, to hold files for configuration, log, counter, and spool. Then create a configuration file named "SMTPGATE/users/recipient/conf".

Example: SMTP to SMTP forwarding

// forward messages accepted at "feedback@delegate.org"
// toward "delegate-en@smtpgate.etl.go.jp"


delegate.org# delegated -P25 SERVER=smtp

[the contents of SMTPGATE/users/feedback/conf]

INHERIT: sendmail
SERVER-HOST: mail.etl.go.jp
RECIPIENT: delegate-en@smtpgate.etl.go.jp
ACCEPT/From: !%, !MAILER_DAEMON@, !hotmail.com, ...

Example: SMTP to NNTP forwarding

[the contents of SMTPGATE/users/feedback/conf]
INHERIT: postnews
SERVER-HOST: news.delegate.org
OUTPUT/Newsgroups: mail-lists.delegate-en
OUTPUT/Distribution: world
OUTPUT/Reply-To: feedback@delegate.org
OUTPUT/Subject: [DeleGate-En] ${subject:hc}
OUTPUT/Header: X-Seqno: ${seqno}
OUTPUT/Header: UNIX-From: ${unixfrom}
CONTROL/Errors-To: mladmin@delegate.org
ACCEPT/User-Text: delegate ## reject if a word "delegate" is not in body
ACCEPT/Max-Bytes: 50000 ## reject larger 50KB header+body
ACCEPT/Min-Body-Bytes: 64 ## reject smaller 64B body
OPTION: isn,rni,res,reb


A SMTPGATE configuration file consists of a series of lines of directives, each looks like a message header of the internet message. Comment string after sharp (#) character in each line is ignored. Directives are categorized into three groups; CONTROL, ACCEPT and OUTPUT.

CONTROL

Specify the function of the gateway, the destination server, and the destination address in the envelope. Note that you can inherit a configuration from another recipient as well as "sendmail" and "postnews" in the INHERIT directive.

INHERIT: {sendmail | postnews | recipient}

SERVER-HOST: host

SERVER-PORT: portNumber

RECIPIENT: EmailAddressForm (used with "sendmail")

CONTROL/SENDER: EmailAddressForm (envelope's From in SMTP)

CONTROL/BCC: EmailAddressForm (a copy is sent to the address on success)

CONTROL/Errors-To: EmailAddress (a copy is sent to the address on error or rejection)

ARCHIVE: archiveFileNameForm

MYAUTH: username:password (AUTHINFO for NNTP server)

OPTION: OptionList

isn -- Increment Sequence Number (to be referred by ${seqno})
rni -- Reject No message-Id
res -- Reject Empty Subject
reb -- Reject Empty Body
axo -- Append X-Original headers
rxo -- Remove X-Original headers
gwt -- GateWay Trace
ntr -- Do NOT add trace field (Received:)

ACCEPT

If specified, only messages which have fields matching with specified patterns are accepted.

ACCEPT/Sender: ListOfEmailAddressPattern

ACCEPT/Recipient: ListOfEmailAddressPattern

ACCEPT/From: ListOfEmailAddressPattern

ACCEPT/To: ListOfEmailAddressPattern

ACCEPT/Max-Bytes: messageSize

ACCEPT/Min-Body-Bytes: bodySize

ACCEPT/Max-Exclams: theNumberOfExclamationMarks

ACCEPT/User-Text: listOfWords (in Subject or body)

REJECT/User-Text: listOfWords (in Subject or body)

ACCEPT/Content-Type: listOfTypesOrCharsets

ACCEPT/Client-Host: srcHostList

OUTPUT

Header fields to be put into the output messages replacing the original fields in the input message.

Newsgroups: fieldBodyForm (to be used with "postnews")

Distribution: fieldBodyForm (to be used with "postnews")

Reply-To: fieldBodyForm

To: fieldBodyForm

Subject: fieldBodyForm

Header: fieldName: fieldBodyForm

FILTER: filterCommand

Substitution

The following patterns appearing in ...Form in field body part of directives are substituted with the values in the header or the envelope of the input message.

${sender} -- sender in the envelope (in RCPT To)

${recipient} -- recipient in the envelope (in MAIL From)

${recipient.name} -- local name part of the recipient

${recipient.mx} -- Mail eXchanger of the recipient

${header.field} -- body of header field in the input message

${from} -- From field in the input message

${unixfrom} -- Unix-From string for the recipient

${subject} -- Subject field in the input message

${subject:hc} -- head-cleaned Subject field

${seqno} -- sequence number

${seqno/10} -- sequence number / 10 (used with ARCHIVE)

${seqno/100} -- sequence number / 100 (used with ARCHIVE)

${date+format} -- formatted string of current time (used with ARCHIVE)

When a SMTP-DeleGate received a message bound for a recipient, with an address formed as recipient@mailhost, it retrieves the configuration file for the recipient in the following two directories in the order.

SMTPGATE/users/recipient/

SMTPGATE/admin/recipient/

If no configuration for the recipient is found, then the default configuration is used if it exists at the following directory.

SMTPGATE/admin/@default/

Otherwise the built-in default configuration is used. The default is at "/-/builtin/config/smtpgate/@default/conf" which can be customized with MOUNT option. The contents of the default is like follows which means just delivering the input message to the address of the recipient via the mail exchanger of the recipient.

CONTROL/INHERIT: sendmail
CONTROL/RECIPIENT: ${recipient}
CONTROL/SERVER-HOST: ${recipient.mx}


The directory for each recipient contains following files.

recipient/conf -- configuration file

recipient/log -- log file

recipient/count -- counter file for ${seqno} (optional)

recipient/spool/ -- archive directory of relayed messages (optional)

recipient/rejected/ -- archive directory of rejected ones (optional)

Optional ones will be enabled by manually creating the file or the directory. Instead of the default archive file, user can define the file name and the unit of archive by ARCHIVE directive.

Example:

ARCHIVE: spool/%05${seqno}-${date+%Y%m%d-%H%M%S}-%05${pid}


## default archive enabled if spool/ exists


ARCHIVE: arc-${seqno} ## archive with sequence number


ARCHIVE: arc-%4${seqno/10} ## an archive file per every 10 messages


ARCHIVE: arc-${date+%Y-%m} ## an archive file per month

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