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9. Virtual Mail/Pop

9.1 Problem

Virtual mail support is in ever increasing demand. Sendmail says it supports virtual mail. What it does support is listening for incoming mail from different domains. You can then specify to have the mail forwarded somewhere. However, if you forward it to the local machine and have incoming mail to bob@domain1.com and bob@domain2.com they will go to the same mail folder. This is a problem since both bob's are different people with different mail.

9.2 Solution

You can make sure that each user name is unique by using a numbering scheme: bob1, bob2, etc or prepending a few characters to each username dom1bob, dom2bob, etc. You could also hack mail and pop to do these conversions behind the scenes but that can get messy. Outgoing mail also has the banner maindomain.com and you want each subdomain's outgoing mail banner to be different.

I have two solutions. One works with sendmail and one works with Qmail. The solution with sendmail should work with a stock install of sendmail. However, it shares all the limitations built into sendmail. It also requires that one sendmail has to be run in queue mode for each domain. Having 50 or more sendmail queue processes that wake up every hour can put a little strain on a machine.

The solution offered with Qmail does not require multiple instances of Qmail and can run out of one queue directory. It does require an extra program since Qmail does not rely on virtuald. I believe a similar procedure can be done with sendmail. However, Qmail lends itself to this solution more readily.

I do not endorse any one program over the other. The sendmail install is a little more straight forward but Qmail is probably the more powerful of the two mail server packages.

9.3 Sendmail Solution

Introduction

Each virtual filesystem gives a domain its own /etc/passwd. This means that bob@domain1.com and bob@domain2.com are different users in different /etc/passwds so mail will be no problem. They also have their own spool directories so the mail folders will be different files on different virtual filesystems.

Create Sendmail Configuration File

Create /etc/sendmail.cf like you would normally through m4. I used:

divert(0)
VERSIONID(`tcpproto.mc')
OSTYPE(linux)
FEATURE(redirect)
FEATURE(always_add_domain)
FEATURE(use_cw_file)
FEATURE(local_procmail)
MAILER(local)
MAILER(smtp)

Edit Sendmail Configuration File

Edit /virtual/domain1.com/etc/sendmail.cf to respond as your virtual domain:

vi /virtual/domain1.com/etc/sendmail.cf # Approximately Line 86 
It should say:

#Dj$w.Foo.COM

Replace it with:

Djdomain1.com

Sendmail Local Delivery

Edit /virtual/domain1.com/etc/sendmail.cw with the local hostnames.

vi /virtual/domain1.com/etc/sendmail.cw
mail.domain1.com
domain1.com
domain1
localhost

Sendmail Between Virtual Domains: The Hack (PRE8.8.6)

However, sendmail requires one minor source code modification. Sendmail has a file called /etc/sendmail.cw and it contains all machine names that sendmail will deliver mail to locally rather than forwarding to another machine. Sendmail does internal checking of all the devices on the machine to initialize this list with the local IPs. This presents a problem if you are mailing between virtual domains on the same machine. Sendmail will be fooled into thinking another virtual domain is a local address and spool the mail locally. For example, bob@domain1.com sends mail to fred@domain2.com. Since domain1.com's sendmail thinks domain2.com is local, it will spool the mail on domain1.com and never send it to domain2.com. You have to modify sendmail (I did this on v8.8.5 without a problem):

vi v8.8.5/src/main.c # Approximately Line 494
It should say:

load_if_names();

Replace it with:

/* load_if_names(); Commented out since hurts virtual */

Note only do this if you need to send mail between virtual domains which I think is probable.

This will fix the problem. However, the main ethernet device eth0 is not removed. Therefore, if you send mail from a virtual IP to the one on eth0 on the same box it will delivery locally. Therefore, I just use this as a dummy IP virtual1.maindomain.com (10.10.10.157). I never send mail to this host so neither will the virtual domains. This is also the IP I would use to ssh into the box to check if the system is ok.

Sendmail Between Virtual Domains: New Sendmail Feature (POST8.8.6)

As of Sendmail V8.8.6, there is a new option to disable loading of the extra network interfaces. This means you do NOT have to alter the code in any way. It is called DontProbeInterfaces .

Edit /virtual/domain1.com/etc/sendmail.cf

vi /virtual/domain1.com/etc/sendmail.cf # Add the line
O DontProbeInterfaces=True

Sendmail.init

Sendmail cannot be started stand alone anymore so you have to run it through inetd. This is inefficient and will result in lower start up time but if you had such a high hit site you would not share it on a virtual box with other domains. Note that you are NOT running with the -bd flag. Also note that you need a sendmail -q running for each domain to queue up undelivered mail. The new sendmail.init file:

#!/bin/sh

. /etc/rc.d/init.d/functions

case "$1" in
  start)
        echo -n "Starting sendmail: "
        daemon sendmail -q1h
        echo
        echo -n "Starting virtual sendmail: "
        for i in /virtual/*
        do
                if [ ! -d "$i" ]
                then
                        continue
                fi
                if [ "$i" = "/virtual/lost+found" ]
                then
                        continue
                fi
                chroot $i sendmail -q1h
                echo -n "."
        done
        echo " done"
        touch /var/lock/subsys/sendmail
        ;;
  stop)
        echo -n "Stopping sendmail: "
        killproc sendmail
        echo
        rm -f /var/lock/subsys/sendmail
        ;;
  *)
        echo "Usage: sendmail {start|stop}"
        exit 1
esac

exit 0

Inetd Setup

Pop should install normally with no extra effort. It will just need the inetd entry for it with the virtuald part added. The inetd.conf entries for sendmail and pop:

pop-3 stream tcp nowait root /usr/local/bin/virtuald \
        virtuald /virtual/conf.pop in.qpop -s 
smtp stream tcp nowait root /usr/local/bin/virtuald \
        virtuald /virtual/conf.mail sendmail -bs

9.4 Qmail Solution

Introduction

This solution takes over the delivery responsibilities of qmail-local, so use of the .qmail files in the virtual home directories will not work. However, each domain will still get a domain master user that will control aliasing for the whole domain. Two external programs will be used for that domain masters .qmail-default file. The mail will be passed through these two programs in order to deliver mail for each domain.

Two programs are required since one of them is run setuid root. It is a small program that changes to a non-root user and then runs the second program. Consult your nearest security related site for a discussion as to why this is necessary.

This solution bypasses the need for using virtuald. Qmail is flexible enough to not require a general virtuald setup. Qmail's design utilizes the chaining of programs together to deliver mail. This design makes it very easy to insert the virtual section into the Qmail delivery process without altering a stock install of Qmail.

A note that since you are using one Qmail any unqualified domain name will be expanded with the domain of the main server. This is because you do not have a separate Qmail server for each domain. Therefore, make sure that your client (Eudora, elm, mutt, etc.) knows to expand all of your unqualified domain names.

Setup Virtual Domains

Qmail has to be configured to accept mail for each of the virtual domains you will be serving. Type the following commands.

echo "domain1.com:domain1" >> /var/qmail/control/virtualdomains

Setup Domain Master User

Add to your main /etc/passwd file the user domain1. I would make the shell /bin/false so that the domain master cannot log in. That user will be able to add .qmail files and all mail for domain1 will route through that account. Note that usernames can only be eight characters long and domain names can be longer. The remaining characters are truncated. That means that user domain12 and domain123 are going to be the same user and Qmail might get confused. So be careful in your master domain user naming convention.

Create the domain master's .qmail files with the following commands. Add any other system aliases at this point. For example, webmaster or hostmaster.

echo "user@domain1.com" > /home/d/domain1/.qmail-mailer-daemon
echo "user@domain1.com" > /home/d/domain1/.qmail-postmaster
echo "user@domain1.com" > /home/d/domain1/.qmail-root

Create the domain master's .qmail-default file. This will filter all mail to the virtual domain.

echo "| /usr/local/bin/virtmailfilter" > /home/d/domain1/.qmail-default

Tcpserver

Qmail requires a special pop that can support the Maildir format. The pop program has to be virtualized. The author of Qmail recommends using tcpserver (an inetd replacement) with Qmail so my examples use tcpserver and NOT inetd.

Tcpserver does not require a config file. All the information can be passed to it via the command line. Here is the tcpserver.init file that you would use for the mail daemon and popper:

#!/bin/sh

. /etc/rc.d/init.d/functions

QMAILDUSER=`grep qmaild /etc/passwd | cut -d: -f3`
QMAILDGROUP=`grep qmaild /etc/passwd | cut -d: -f4`

# See how we were called.
case "$1" in
  start)
        echo -n "Starting tcpserver: "
        tcpserver -u 0 -g 0 0 pop-3 /usr/local/bin/virtuald \
                /virtual/conf.pop qmail-popup virt.domain1.com \
                /bin/checkpassword /bin/qmail-pop3d Maildir &
        echo -n "pop "  
        tcpserver -u $QMAILDUSER -g $QMAILDGROUP 0 smtp \
                /var/qmail/bin/qmail-smtpd &
        echo -n "qmail "
        echo
        touch /var/lock/subsys/tcpserver
        ;;
  stop)
        echo -n "Stopping tcpserver: "
        killall -TERM tcpserver 
        echo -n "killing "
        echo 
        rm -f /var/lock/subsys/tcpserver
        ;;
  *)
        echo "Usage: tcpserver {start|stop}"
        exit 1
esac

exit 0

Qmail.init

You can use the standard Qmail init script provided. Qmail comes with very good documentation describing how to set this up.

Source

You require two other programs to get virtual mail working with Qmail. They are virtmailfilter and virtmaildelivery. This is the C source to virtmailfilter. It should be installed in /usr/local/bin with permissions 4750, user root, and group nofiles.

#include <sys/wait.h>
#include <unistd.h>
#include <string.h>
#include <stdlib.h>
#include <stdio.h>
#include <ctype.h>
#include <pwd.h>

#define VIRTPRE                 "/virtual"

#define VIRTPWFILE              "etc/passwd"
#define VIRTDELIVERY            "/usr/local/bin/virtmaildelivery"
#define VIRTDELIVERY0           "virtmaildelivery"

#define PERM                    100
#define TEMP                    111
#define BUFSIZE                 8192

int main(int argc,char **argv)
{
        char *username,*usernameptr,*domain,*domainptr,*homedir;
        char virtpath[BUFSIZE];
        struct passwd *p;
        FILE *fppw;
        int status;
        gid_t gid;
        pid_t pid;

        if (!(username=getenv("EXT")))
        {
                fprintf(stdout,"environment variable EXT not set\n");
                exit(TEMP);
        }

        for(usernameptr=username;*usernameptr;usernameptr++)
        {
                *usernameptr=tolower(*usernameptr);
        }

        if (!(domain=getenv("HOST")))
        {
                fprintf(stdout,"environment variable HOST not set\n");
                exit(TEMP);
        }

        for(domainptr=domain;*domainptr;domainptr++)
        {
                if (*domainptr=='.' && *(domainptr+1)=='.')
                {
                        fprintf(stdout,"environment variable HOST has ..\n");
                        exit(TEMP);
                }
                if (*domainptr=='/')
                {
                        fprintf(stdout,"environment variable HOST has /\n");
                        exit(TEMP);
                }

                *domainptr=tolower(*domainptr);
        }

        for(domainptr=domain;;)
        {
                snprintf(virtpath,BUFSIZE,"%s/%s",VIRTPRE,domainptr);
                if (chdir(virtpath)>=0)
                        break;

                if (!(domainptr=strchr(domainptr,'.')))
                {
                        fprintf(stdout,"domain failed: %s\n",domain);
                        exit(TEMP);
                }

                domainptr++;
        }

        if (!(fppw=fopen(VIRTPWFILE,"r+")))
        {
                fprintf(stdout,"fopen failed: %s\n",VIRTPWFILE);
                exit(TEMP);
        }

        while((p=fgetpwent(fppw))!=NULL)
        {
                if (!strcmp(p->pw_name,username))
                        break;
        }

        if (!p)
        {
                fprintf(stdout,"user %s: not exist\n",username);
                exit(PERM);
        }

        if (fclose(fppw)==EOF)
        {
                fprintf(stdout,"fclose failed\n");
                exit(TEMP);
        }

        gid=p->pw_gid;
        homedir=p->pw_dir;

        if (setgid(gid)<0 || setuid(p->pw_uid)<0)
        {
                fprintf(stdout,"setuid/setgid failed\n");
                exit(TEMP);
        }

        switch(pid=fork())
        {
                case -1:
                        fprintf(stdout,"fork failed\n");
                        exit(TEMP);
                case 0:
                        if (execl(VIRTDELIVERY,VIRTDELIVERY0,username,homedir,NULL)<0)
                        {
                                fprintf(stdout,"execl failed\n");
                                exit(TEMP);
                        }
                default:
                        if (wait(&status)<0)
                        {
                                fprintf(stdout,"wait failed\n");
                                exit(TEMP);
                        }
                        if (!WIFEXITED(status))
                        {
                                fprintf(stdout,"child did not exit normally\n");
                                exit(TEMP);
                        }
                        break;
        }

        exit(WEXITSTATUS(status));
}

Source

You require two other programs to get virtual mail working with Qmail. They are virtmailfilter and virtmaildelivery. This is the C source to virtmaildelivery. It should be installed in /usr/local/bin with permissions 0755, user root, and group root.

#include <sys/stat.h>
#include <sys/file.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <stdio.h>
#include <errno.h>
#include <time.h>

#define TEMP                    111
#define BUFSIZE                 8192
#define ATTEMPTS                10

int main(int argc,char **argv)
{
        char *user,*homedir,*dtline,*rpline,buffer[BUFSIZE],*p,mail[BUFSIZE];
        char maildir[BUFSIZE],newmaildir[BUFSIZE],host[BUFSIZE];
        int fd,n,nl,i,retval;
        struct stat statp;
        time_t thetime;
        pid_t pid;
        FILE *fp;

        retval=0;

        if (!argv[1])
        {
                fprintf(stdout,"invalid arguments: need username\n");
                exit(TEMP);
        }

        user=argv[1];

        if (!argv[2])
        {
                fprintf(stdout,"invalid arguments: need home directory\n");
                exit(TEMP);
        }

        homedir=argv[2];

        if (!(dtline=getenv("DTLINE")))
        {
                fprintf(stdout,"environment variable DTLINE not set\n");
                exit(TEMP);
        }

        if (!(rpline=getenv("RPLINE")))
        {
                fprintf(stdout,"environment variable RPLINE not set\n");
                exit(TEMP);
        }

        while (*homedir=='/')
                homedir++;
        snprintf(maildir,BUFSIZE,"%s/Maildir",homedir);
        if (chdir(maildir)<0)
        {
                fprintf(stdout,"chdir failed: %s\n",maildir);
                exit(TEMP);
        }

        time(&thetime);
        pid=getpid();
        if (gethostname(host,BUFSIZE)<0)
        {
                fprintf(stdout,"gethostname failed\n");
                exit(TEMP);
        }

        for(i=0;i<ATTEMPTS;i++)
        {
                snprintf(mail,BUFSIZE,"tmp/%u.%d.%s",thetime,pid,host);
                errno=0;
                stat(mail,&statp);
                if (errno==ENOENT)
                        break;

                sleep(2);
                time(&thetime);
        }
        if (i>=ATTEMPTS)
        {
                fprintf(stdout,"could not create %s\n",mail);
                exit(TEMP);
        }

        if (!(fp=fopen(mail,"w+")))
        {
                fprintf(stdout,"fopen failed: %s\n",mail);
                retval=TEMP; goto unlinkit;
        }

        fd=fileno(fp);

        if (fprintf(fp,"%s",rpline)<0)
        {
                fprintf(stdout,"fprintf failed\n");
                retval=TEMP; goto unlinkit;
        }

        if (fprintf(fp,"%s",dtline)<0)
        {
                fprintf(stdout,"fprintf failed\n");
                retval=TEMP; goto unlinkit;
        }

        while(fgets(buffer,BUFSIZE,stdin))
        {
                for(p=buffer;*p=='>';p++)
                        ;

                if (!strncmp(p,"From ",5))
                {
                        if (fputc('>',fp)<0)
                        {
                                fprintf(stdout,"fputc failed\n");
                                retval=TEMP; goto unlinkit;
                        }
                }

                if (fprintf(fp,"%s",buffer)<0)
                {
                        fprintf(stdout,"fprintf failed\n");
                        retval=TEMP; goto unlinkit;
                }
        }

        p=buffer+strlen(buffer);
        nl=2;
        if (*p=='\n')
                nl=1;

        for(n=0;n<nl;n++)
        {
                if (fputc('\n',fp)<0)
                {
                        fprintf(stdout,"fputc failed\n");
                        retval=TEMP; goto unlinkit;
                }
        }

        if (fsync(fd)<0)
        {
                fprintf(stdout,"fsync failed\n");
                retval=TEMP; goto unlinkit;
        }

        if (fclose(fp)==EOF)
        {
                fprintf(stdout,"fclose failed\n");
                retval=TEMP; goto unlinkit;
        }

        snprintf(newmaildir,BUFSIZE,"new/%u.%d.%s",thetime,pid,host);
        if (link(mail,newmaildir)<0)
        {
                fprintf(stdout,"link failed: %s %s\n",mail,newmaildir);
                retval=TEMP; goto unlinkit;
        }

unlinkit:
        if (unlink(mail)<0)
        {
                fprintf(stdout,"unlink failed: %s\n",mail);
                retval=TEMP;
        }

        exit(retval);
}

9.5 Acknowledgement

Thank you Vicente Gonzalez (vince@nycrc.net) for helping make the Qmail solution possible. You can certainly mail your thanks to Vince, however all questions and comments including issues regarding Qmail, about this HOWTO should continue to be directed to me.


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