Simple SMTP server for alias based forwarding

emailmail-forwardingpostfixsmtp

I'm looking for a SMTP server that will just be used to forward a few email addresses. Two requirements:

  1. Easy to install and configure on Ubuntu.
  2. Has an aliases file that is easy to automatically add to. Ideally, it would be a text file consisting of rows like "foo@myserver.com mrfoo@gmail.com".
  3. (Ideally) Can be easily configured to only accept mail from specific hosts.

I've been trying Postfix, but I'm getting bogged down in error messages like Recipient address rejected: User unknown in virtual alias table and Recipient address rejected: User unknown in local recipient table. So I wonder if there is an easier solution.

Best Answer

  1. Use Postfix

    On ubuntu, do following

    apt-get install postfix

    I am doing the exact same thing with my vps email setup. check up my blog post Tiny VPS Postfix. I am copying the example below

    /etc/postfix/main.cf

    # See /usr/share/postfix/main.cf.dist for a commented, more complete version

# Debian specific:  Specifying a file name will cause the first
# line of that file to be used as the name.  The Debian default
# is /etc/mailname.
#myorigin = /etc/mailname

smtpd_banner = $myhostname ESMTP $mail_name (Ubuntu)
biff = no

# appending .domain is the MUA's job.
append_dot_mydomain = no

# Uncomment the next line to generate "delayed mail" warnings
#delay_warning_time = 4h

readme_directory = no

# TLS parameters
smtpd_tls_cert_file=/etc/ssl/certs/ssl-cert-snakeoil.pem
smtpd_tls_key_file=/etc/ssl/private/ssl-cert-snakeoil.key
smtpd_use_tls=yes
smtpd_tls_session_cache_database = btree:${data_directory}/smtpd_scache
smtp_tls_session_cache_database = btree:${data_directory}/smtp_scache

# See /usr/share/doc/postfix/TLS_README.gz in the postfix-doc package for
# information on enabling SSL in the smtp client.

myhostname = <YOUR HOSTNAME>
alias_maps = hash:/etc/aliases
alias_database = hash:/etc/aliases
myorigin = /etc/mailname
mydestination = <YOUR DOMAIN NAME>, localhost.domain, localhost
relayhost =
mynetworks = 127.0.0.0/8 [::ffff:127.0.0.0]/104 [::1]/128
mailbox_command = procmail -a "$EXTENSION"
mailbox_size_limit = 0
recipient_delimiter = +
inet_interfaces = all

smtpd_recipient_restrictions =
    permit_mynetworks,
    permit_sasl_authenticated,
    reject_invalid_hostname,
    reject_non_fqdn_hostname,
    reject_non_fqdn_sender,
    reject_non_fqdn_recipient,
    reject_unknown_recipient_domain,
    reject_unlisted_recipient,
    reject_unauth_destination,
    reject_rbl_client cbl.abuseat.org,
    reject_rbl_client bl.spamcop.net,
    reject_rbl_client relays.mail-abuse.org,
    reject_rbl_client dnsbl.proxybl.org,
    reject_rbl_client truncate.gbudb.net,
    reject_rbl_client dnsbl.njabl.org,
    permit

    Remeber to change <YOUR HOSTNAME> and <YOUR DOMAIN NAME>

  2. Alias file

    Your /etc/aliases file should be like the following

    foo: mrfoo@gmail.com
bar: mrbar@gmail.com

    The left hand side should have no domain name, only username. The domain is control by your postfix configuration. then do following

    cd /etc
postalias aliases
service postfix restart

  3. Single host restriction

    To allow only email from a single(or a few) host, I am going to use a very lazy way to do it.

    Assuming the IP of the allowed incoming host has IP 192.168.1.100, add it to mynetworks

    mynetworks = 127.0.0.0/8 [::ffff:127.0.0.0]/104 [::1]/128 192.168.1.100

    Change smtpd_recipient_restrictions to following

    smtpd_recipient_restrictions =
    permit_mynetworks,
    reject_unlisted_recipient

    Postfix only (and always) accept email from host(s) listed in mynetworks. And reject everything else.

  4. DNS Configuration

    Remember to setup MX record and spf record.

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