Postfix virtual users forwarding

2008.04.06 @22:18

		I've reinstalled completely my mail server with :

    postfix
    dovecot
    ClamAV
    ClamSMTP
    postgrey
    spam assassin
    squirrelmail

Following these great articles. By the way in the first article, be sure you changed ownership of /home/vmail and everything below (domains etc...) to the vmail user or at least for him to rwx. If not your email will bounce to the recipient with the corresponding error message (something like "file or directory not found").
Everything worked as expected and quite quickly under ubuntu I must say... until I wanted to give to my users the same forwarding possibility as before (with qmail). With virtual users for some obscure security reasons (??), you cannot use the .forward (or .qmail) files !

"This agent was originally based on the Postfix local delivery agent. Modifications mainly consisted of removing code that either was not applicable or that was not safe in this context: aliases, ~user/.forward files, delivery to "|command" or to /file/name " from the postfix documentation.

Well in your /etc/postfix/vmaps you can specify redirections (john@doe.com -> johndoe@gmail.com) but you cannot save the email and forward it to one or more addresses like we often do for small mailing lists on "general" email addresses such as "contact@example.com"
As it seems it is not that easy to find a solution to this surprisingly bigger-than-I-thought small problem ! I haven't found  anything about this on internet. It's probably resolvable if you choose to store your emails in mysql (although I didnt try) but I like the old filesystem style better, easier for external scripting and it doesnt bother the database.
So I wrote a transport layer who does this. I hope it could be useful to someone.
Features :

    no need to install an external program and should work with any postfix/imap/pop3 installation
    deliver mails locally and/or forward to as many as addresses as you wish
    supports aliases
    if you use spam assassin (or another antispam which follows the same marking rules), the script can dispose automatically of your spam (delete or putting them to a server blackhole directory)

To install it :

    edit  /etc/postfix/main.cf and change : virtual_transport = mydrop
    comment your transport_maps line if any
    edit  /etc/postfix/master.cf and add at the end (there should be no spaces at the end of the lines)

mydrop    unix  -       n       n       -       -       pipe
        user=vmail argv=/home/vmail/mydrop.py -d ${recipient}

    put the following script in /home/vmail/mydrop.py  and configure if needed the options at the top
    chmod +x /home/vmail/mydrop.py 
    restart postfix with:  /etc/init.d/postfix restart

To use it :
By default it will deliver to the /home/vmail/domain/johndoe/ directories as before.

At any time you can create a ".qmail" file in each of the account's root (such as /home/vmail/domain/johndoe/) and as per the ususal .qmail files you can use on each line either "&johndoe@gmail.com" to forward to this email or "./Maildir/" (case insentive) to deliver locally. Example to forward to 2 addresses and keep locally :
&johndoe@gmail.com
&there@example.com
./Maildir/

 Let me know if you have any questions...
Note : you need to have all your domains and users to be in lowercase in your directories and your vmaps or you wont be able to receive emails in capitals.
[NOTE this has been updated on 4th of september 2008 to fix a bug] mydrop.py script :
#!/usr/bin/python

import sys
import os
import time
import commands
import shutil

# BEGIN - configuration
VMAILROOT = '/home/vmail/'           # root of all virtual domain directories
VMAPS = '/etc/postfix/vmaps'         # the postfix aliases mapping
SENDMAILPATH = '/usr/sbin/sendmail'  # path to sendmail or sendmail replacement
SPAM_TRIGGER = 1 # 0 = do nothing more on spam or I dont use spam assassin
                 # 1 = BLACKHOLE obvious spam detected by spam-assassin
                 # 2 = delete obvious spam detected by spam-assassin
SPAM_OBVIOUS_LEVEL = 10              # obvious spam are > at this spam level
SPAM_BLACKHOLE = '/home/vmail/SPAM/' # directory you want to save the obvious SPAM instead
TMP = '/tmp/'
# END - configuration

class MyDropError(Exception): pass

def findEmptyFile(fileName):
    # be sure it doesnt exist already by bad luck
    while 1:
        try:
            os.stat(fileName)
        except:
            break
        fileName += '_'
    return fileName

def goToDestination(dest):
    # get user and domain from the argument
    domain=dest.split('@')[1]
    user=dest.split('@')[0]
    # the user has to be found in this mapping otherwise postfix couldnt deliver the email
    try:
        user=aliases[dest].split('/')[1]
        domain=aliases[dest].split('/')[0]
    except:
        raise MyDropError, 'User '+dest+' doesnt exist'
        #if domain=='lacde.net':
        #    user='arluison'

    directNEW=VMAILROOT+domain+'/'+user+'/new/'
    try:
        os.stat(directNEW)
    except:
        raise IOError, 'Directories for this user are not created'

    else:
        # deliver the email
        # now try to read the .qmail equivalent if available
        dotqmail=VMAILROOT+domain+'/'+user+'/.qmail'
        keepLocally=1
        try:
            g=open(dotqmail)
            keepLocally=0
            for s in g.readlines():
                if s.lower().startswith('./maildir'):
                    # deliver locally
                    keepLocally=1
                elif s.startswith('&'):
                    # send the email elsewhere
                    commands.getoutput(SENDMAILPATH + ' ' + s[1:].strip() + ' < '+fileName)

        except IOError, e:
            if e[0]!=2:
                # if anything else than "no such file or directory"
                raise e
            # file not found = nothing has been configured, fair enough
            keepLocally=1

        # keep locally or not
        if keepLocally:
            destName=findEmptyFile(directNEW + tagName)
            shutil.copy(fileName, destName)

# Program itself
# call from postfix will look like that :
# mydrop.py -d test@example.com
# and stdin will be filled with the email

l=len(sys.argv)
destinations=None

for i in xrange(l):
    if sys.argv[i]=='-d':
        destinations=sys.argv[i+1:]
        break

if not destinations:
    raise Error, 'Lack of destination, giving up, mydrop wrongly configured'

# will check if user is not an alias
adrList=open(VMAPS).read().split()
aliases={}
for i in xrange(0, len(adrList)/2):
    aliases[adrList[i*2]]=adrList[i*2+1]

isBigSpam=0
strCheck='X-Spam-Level: '+'*'*SPAM_OBVIOUS_LEVEL
continueCheck=1

# write the email to the temporary file
tagName=str(time.time()) + '_' + str(os.getpid())
fileName=findEmptyFile(TMP + 'tmpMail_' + tagName)
g=open(fileName, 'w')
for s in sys.stdin.readlines():
    g.write(s)
    # check if line looks like : 'X-Spam-Level: **********'
    if continueCheck:
        if s.startswith(strCheck):
            isBigSpam=1
            continueCheck=0
        if s=='\n' or s=='\r\n':
            # ok end of headers
            continueCheck=0
g.close()

if SPAM_TRIGGER and isBigSpam:
    if SPAM_TRIGGER==1:
        # move to server SPAM blackhole
        destName=findEmptyFile(SPAM_BLACKHOLE + tagName)
        os.rename(fileName, destName)
    else:
        os.remove(fileName)
else:
    # deliver the email normally
    errors = []
    for dest in destinations:
        try:
            goToDestination(dest.lower())
        except Exception, e:
            errors.append(e)
    os.remove(fileName)
    if len(errors):
        raise MyDropError, 'Sorry :' + str(len(errors)) + ' error(s) occured :\n' + str(errors)