Tcp.smtp: Difference between revisions

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Your default tcp.smtp file on a fresh install looks like this (backslashes are for display purposes only, do not include them or newlines or extra spaces in the file - there are two and only two lines here):
Your default tcp.smtp file on a fresh install looks like this (backslashes are for display purposes only, do not include them or newlines or extra spaces in the file - there are two and only two lines here):


127.:allow,RELAYCLIENT="",RBLSMTPD="",NOP0FCHECK="1"
127.:allow,RELAYCLIENT=""
<nowiki>:</nowiki>allow,BADMIMETYPE="",BADLOADERTYPE="M",CHKUSER_RCPTLIMIT="50",CHKUSER_WRONGRCPTLIMIT="10",QMAILQUEUE="/var/qmail/bin/simscan",NOP0FCHECK="1"
<nowiki>:</nowiki>allow,BADMIMETYPE="",BADLOADERTYPE="M",CHKUSER_RCPTLIMIT="50",CHKUSER_WRONGRCPTLIMIT="10",QMAILQUEUE="/var/qmail/bin/simscan"


Line 1
Line 1
    127.:allow - Allow localhost
127.:allow - Allow localhost
  RELAYCLIENT="" - Allow relaying without authentication
  RELAYCLIENT="" - Allow relaying without authentication
    RBLSMTPD="" -
NOP0FCHECK="1" -


Line 2
Line 2


                      (empty):allow -  
(empty):allow - Allow remote to deliver locally, no relay
                      BADMIMETYPE="" -  
BADMIMETYPE="" - Warlord patch
                  BADLOADERTYPE="M" -  
BADLOADERTYPE="M" - Warlord patch
              CHKUSER_RCPTLIMIT="50" -  
CHKUSER_RCPTLIMIT="50" - Max recipients any more are denied
        CHKUSER_WRONGRCPTLIMIT="10" -  
CHKUSER_WRONGRCPTLIMIT="10" - Max non-existent recipients any more denied
  QMAILQUEUE="/var/qmail/bin/simscan" -  
  QMAILQUEUE="/var/qmail/bin/simscan" - Simscan is the queue and will call qmail-queue
                      NOP0FCHECK="1" -  


[https://cr.yp.to/ucspi-tcp/tcprules.html tcprules]


'''Let's break that down.''' Entries in the default tcp.smtp and what they mean:
# tcprulescheck tcp.smtp.cdb
 
  rule :
line 1)
set environment variable SIMSCAN_DEBUG=1
 
  set environment variable SMTP_DEBUG=1
127.     ->local (as in 127.0.0.1)
  set environment variable DSPAM_BIN=/usr/bin/dspamc
 
  set environment variable DSPAM_DEBUG=1
  :     ->if, then or 'default follows'
  set environment variable BADMIMETYPE=
 
set environment variable BADLOADERTYPE=M
allow ->instruction to allow,
set environment variable CHKUSER_RCPTLIMIT=50
 
set environment variable CHKUSER_WRONGRCPTLIMIT=10
RELAYCLIENT="" ->variable set to null, calls smtp-auth, never seen it written any other way
  set environment variable QMAILQUEUE=/var/qmail/bin/simscan
 
  allow connection
DKSIGN="/var/qmail/control/domainkeys/%/private"    ->domain key processing instructions to sign mail with dk
 
    '''Putting it all together:'''
  if the incoming mail is local (127.)
then allow relay
process by variable (smtp-auth)
and sign the message with the domain key info.
 
 
line 2)
 
  :    ->if, then--since it is empty(nothing to the left) all mail not meeting      the line 1) conditional is processed by the following rules which are the default.
  allow ->instruction to allow
  BADMIMETYPE=""    ->warlord patch variable--it's fine as-is
  BADLOADERTYPE="M"    ->warlord patch variable--it's fine as-is
  CHKUSER_RCPTLIMIT="15"  -> set max # of recipients, more than this set number, the toaster treats it as a 'mail-bomb-event' and denies further delivery attempts
  CHKUSER_WRONGRCPTLIMIT="3"    -> set max # of non-existant users, once this number is met, the toaster treats it as a 'mail-bomb-event' and denies further delivery attempts
  DKVERIFY="DEGIJKfh"    ->instructions by which to verify domain keys
  QMAILQUEUE="/var/qmail/bin/simscan"    ->instuction how and where to run it through simscan (thus spam/clam/attach) before delivery
  DKQUEUE="/var/qmail/bin/qmail-queue.orig"    ->instruction for where to queue messages for domain key verification.
  DKSIGN="/var/qmail/control/domainkeys/%/private"    ->instruction for location for domain key verification of private key.
 
 
    '''Putting it all together:'''
  Mail making it this far (line 2 of 2) is not local therefore from a remote server, so process it this way as default handling:
check for bad mimetypes
check for badloader types
check for max recipients
check for incorrect addressees
then deliver to the recipient.
Wow, that is a lot to master.
 
 
 
 
 
Now let's talk about customizations.  The default install is very good with very sane defaults for setting up a standalone mail server,
which explains the popularity with not-so-experienced admins such as myself.
Easy to setup, secure by design, secure on setup, wonderfully protective of your valuable emails.  You really want to mess with that?
Please keep an accurate record of your customizations for your sanity. 
The more you customize, the more "on your own" you go.
 
'''I don't have domainkeys setup for [insert reason here]'''
 
Make a copy of tcp.smtp to something like tcp.smtp.dk, in case you change your mind later, then edit out any reference to domainkeys in the tcp.smtp file, then execute:  #qmailctl cdb
 
Warning: no domainkey=Yahoo!/bulk (and possibly other sites)  Your mail will go straight to the bulk folder, unless the recipient 'whitelists' your sender by adding to the contacts list.
 
'''I am confused about badmimetypes/badloaders and simscan...they overlap'''
 
Well, they differ in that simscan uses ripmime to check against file extensions only, whereas badmimetypes/badloaders checks against "known"(to somebody) mime signatures.  The difference is subtle, yet they both block attachments and notify the sender.  If you feel compelled to remove badmimetypes/badloaders from your simscan regimen, then copy the tcp.smtp file to something like tcp.smtp.blbm, in case you change your mind later, then edit out any reference to badloaders and badmimetypes in the tcp.smtp file, then execute:  #qmailctl cdb
(alternatively: you could leave tcp.smtp alone and comment out all lines in these 2 files and execute:  #qmailctrl cdb)
 
'''I want to scan even local mails (clam, spam, attach) as a further protection for my windows users.  You know, to keep them from infecting each other.'''
Add (,QMAILQUEUE="/var/qmail/bin/simscan") without parentheses() to the end of line 1).  Execute:  #qmailctl cdb
     
Now mail from user1-at-domain3-dot-com will process through simscan before it is delivered to user2-at-domain3-dot-com. Also,  mail from user1-at-domain3-dot-com will process through simscan before it is delivered to user3-at-domain2-dot-com on the same toaster.  Interestingly, simscan will scan that message for attachments and viruses, though not for spam.  I believe that has something to do with the RELAYCLIENT variable or the 127 conditional.  This is not something you should worry too much about. If you suspect you are harboring a spammer or a zombie on your domain, pull the plug on the account.
 
 
...to be re-formatted and continued.

Latest revision as of 15:08, 19 October 2024

Back
/etc/tcprules.d/tcp.smtp is a 2 line (default toaster) file that orchestrates many of the QMT functions. It is the traffic cop in a busy intersection, controlling SMTP processing alternatives.

If you're running another MTA in concert with QmailToaster, or you have an unusual or complicated setup, the following might not be applicable to you. If that is the case, you should take your problem straight to the mailing list. Hopefully this page will eventually cover advanced configurations as documented by those who have such requirements.

Reminder: if you make changes to tcp.smtp, execute the following afterwards to activate the changes: 

 # qmailctl cdb

You do not need to stop and start qmail when only regenerating the .cdb files.

Stock (default) tcp.smtp file Your default tcp.smtp file on a fresh install looks like this (backslashes are for display purposes only, do not include them or newlines or extra spaces in the file - there are two and only two lines here): 

127.:allow,RELAYCLIENT=""
:allow,BADMIMETYPE="",BADLOADERTYPE="M",CHKUSER_RCPTLIMIT="50",CHKUSER_WRONGRCPTLIMIT="10",QMAILQUEUE="/var/qmail/bin/simscan"

Line 1 

127.:allow - Allow localhost
RELAYCLIENT="" - Allow relaying without authentication

Line 2 

(empty):allow - Allow remote to deliver locally, no relay
BADMIMETYPE="" - Warlord patch
BADLOADERTYPE="M" - Warlord patch
CHKUSER_RCPTLIMIT="50" - Max recipients any more are denied
CHKUSER_WRONGRCPTLIMIT="10" - Max non-existent recipients any more denied
QMAILQUEUE="/var/qmail/bin/simscan" - Simscan is the queue and will call qmail-queue

tcprules 

# tcprulescheck tcp.smtp.cdb
rule :
set environment variable SIMSCAN_DEBUG=1
set environment variable SMTP_DEBUG=1
set environment variable DSPAM_BIN=/usr/bin/dspamc
set environment variable DSPAM_DEBUG=1
set environment variable BADMIMETYPE=
set environment variable BADLOADERTYPE=M
set environment variable CHKUSER_RCPTLIMIT=50
set environment variable CHKUSER_WRONGRCPTLIMIT=10
set environment variable QMAILQUEUE=/var/qmail/bin/simscan
allow connection
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