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emailler/README-gmail-gateway.md
Bobbi Webber-Manners d1505f114a More updates to README-gmail-gateway.md
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Gmail Apple II Email Gateway

Motivation

To connect an Apple II to Gmail, allowing messages to be sent and received.

I originally set up this gateway to use Ewen Wannop (aka Speccie)'s SAM2 email client, running on the Apple IIgs under GSOS 6.0.4. Speccie's website is here

The same gateway setup also works for my very own Emai//er suite for the Apple //e and IIgs. You can find Emai//er here

In order to communicate on today's Internet Transport Layer Security (TLS) is necessary. Retro machines such as the Apple II series lack the processor power to perform the necessary encryption, so it is necessary to have a proxy system in between the Apple II and Gmail's servers. This proxy machine can 'speak' in today's encrypted TLS protocols to Gmail, and in plaintext to our Apple II. I chose to use a Raspberry Pi 4 (2GB version) running the Raspbian Linux operating system version 10.

Prerequisites

  • For Emai//er on the //e or GS:
    • An Apple //e enhanced or Apple IIgs system (ROM01 or ROM03)
    • At least 128KB of system memory.
    • Enough disk space. I have a MicroDrive/Turbo with 32MB volumes.
    • Uthernet II ethernet card. No other cards are supported.
    • ProDOS. I am using version 2.4.2.
  • or, for SAM2 email on the GS:
    • An Apple IIgs. Mine is a ROM01.
    • Enough memory I have a 4MB RAM card.
    • Enough disk space. I have a MicroDrive/Turbo with 32MB volumes.
    • A compatible ethernet card. I used an Uthernet II.
    • GSOS 6.0.1 or 6.0.4 installed.
    • Marinetti 3.0 installed. I used 3.0b11.
  • A Raspberry Pi running Raspbian 10

I don't cover any of the above in this README. You can find information elsewhere on how to set up Marinetti.

Software Used

I use three separate packages on the Raspberry Pi, as follows:

  • Postfix This is a full-featured mail tranfer agent. We will use it to send mail to the Gmail servers over the SMTPS port with TLS, and to act as a plaintext SMTP server for the local network.
  • Fetchmail Fetchmail is configured to pull down messages from a Gmail inbox and store it on the Raspberry Pi in /var/mail/ using the IMAP protocol with TLS.
  • Dovecot Dovecot provides a POP3 server to the local network, serving the files in /var/mail.

Principle of Operation

Incoming Messages

  • Message is sent to Gmail username@gmail.com
  • Fetchmail runs as a service on the Pi and monitors Gmail using IMAP IDLE. As soon as a message shows up in the INBOX it downloads it and places it in /var/mail/pi (for username pi). Fetchmail leaves the email on the Gmail server (this can be changed if desired.)
  • SAM2 mail client on the Apple IIgs is configured to use the IP of the Raspberry Pi as its POP3 email server. When it asks for new messages, Dovecot will serve the request on port 110. When messages are downloaded using POP3, they are deleted from /var/mail/pi on the Raspberry Pi.

Outgoing Messages

  • The SAM2 mail client on the Apple IIgs is configured to use the IP of the Raspberry Pi as its SMTP server. Outgoing emails are sent to port 25 on the Raspberry Pi.
  • Postfix handles the plaintext SMTP dialog with SAM2 mail and relays the message to Gmail's servers using SMTPS with TLS.

Installing the Packages on Rasbian

Install the packages with root privs on the Pi:

sudo apt update
sudo apt upgrade
sudo apt install postfix postfix-pcre
sudo apt install dovecot-common dovecot-pop3d
sudo apt install fetchmail

Obtaining App Passwords from Google

Google provides a mechanism to allow non-Google apps to connect to Gmail called App Passwords.

Google's help page is here

In order to use the App Passwords method of authentication 2-Step Verification must be turned on for the account. This is the general approach:

  • In a web browser log in to the Gmail account and go to Google Account.
  • In the panel on the left, choose Security.
  • Enable 2-Step Verification for the account.
  • The option App Passwords will now appear. Select this option.
  • At the bottom, choose Select app and enter a descriptive name for the app.
  • Choose Select Device and choose the device.
  • Click Generate.
  • A 16 character App Password will be shown on the screen. Write this value down because you will need it later in the configuration.

I generated two separate App Passwords - one for SMTPS and one for IMAPS.

Configuring the Packages

Postfix

The Postfix MTA configuration files are in /etc/postfix. Of the three packages, Postfix is the most complex to configure and has many available options.

This page was helpful for configuring Postfix.

Be aware that this configuration amounts to an open relay from unsecured SMTP to SMTPS, and must never be place on the public internet, or it will be abused by spammers! Keep it on your private LAN segment only!

We will modify a number of configuration files:

  • /etc/postfix/command_filter
  • /etc/postfix/main.cf
  • /etc/postfix/master.cf
  • /etc/postfix/sasl/sasl_passwd
  • /etc/postfix/sasl/sasl_passwd.db

Once Dovecot has been configured, the service may be controlled as follows:

  • systemctl start postfix - start service.
  • systemctl stop postfix - stop service.
  • systemctl status postfix - status of service.

command_filter

For some reason, SAM2 sends a bunch of mail headers after the email message has been tranmitted to Postfix's SMTP server. Postfix gets very unhappy about this. The solution is to filter them out using Postfix's smtpd_command_filter function.

The command_filter files contains the regular expressions to filter out these unwanted headers:

/^Message-ID:.*$/ NOOP
/^MIME-version:.*$/ NOOP
/^Content-Type:.*$/ NOOP
/^Content-transfer-encoding:.*$/ NOOP
/^From:.*$/ NOOP
/^To:.*$/ NOOP
/^In-Reply-To:.*$/ NOOP
/^Subject:.*$/ NOOP
/^Date:.*$/ NOOP
/^X-Mailer:.*$/ NOOP

main.cf

This is the main Postfix configuration file.

I adjusted smtpd_use_tls = no to turn off TLS for the SMTP service offered to the Apple II and added smtpd_command_filter = pcre:/etc/postfix/command_filter to activate the filter discussed above.

relayhost = [smtp.gmail.com]:587 will forward email to Gmail's SMTPS server.

I adjusted smtpd_relay_restrictions = permit_mynetworks permit_sasl_authenticated defer_unauth_destination to allow network hosts listed in mynetworks to relay messages to the relayhost.

My home network is 192.168.10.0/24, so I added it here: mynetworks = 192.168.10.0/24 127.0.0.0/8 [::ffff:127.0.0.0]/104 [::1]/128. You should adjust this line to match your own LAN subnet.

Finally I added the following block of settings to enabled SASL authentication when talking to Gmail:

# Enable SASL authentication
smtp_sasl_auth_enable = yes
# Disallow methods that allow anonymous authentication
smtp_sasl_security_options = noanonymous
# Location of sasl_passwd
smtp_sasl_password_maps = hash:/etc/postfix/sasl/sasl_passwd
# Enable STARTTLS encryption
smtp_tls_security_level = encrypt
# Location of CA certificates
smtp_tls_CAfile = /etc/ssl/certs/ca-certificates.crt

The whole thing looks like this:

# 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 (Raspbian)
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

# See http://www.postfix.org/COMPATIBILITY_README.html -- default to 2 on
# fresh installs.
compatibility_level = 2

# 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=no
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.

relayhost = [smtp.gmail.com]:587
smtpd_command_filter = pcre:/etc/postfix/command_filter
smtpd_relay_restrictions = permit_mynetworks permit_sasl_authenticated defer_unauth_destination
#smtpd_recipient_restrictions = permit_mynetworks
myhostname = raspberrypi.home
alias_maps = hash:/etc/aliases
alias_database = hash:/etc/aliases
mydestination = $myhostname, raspberrypi, localhost.localdomain, , localhost
mynetworks = 192.168.10.0/24 127.0.0.0/8 [::ffff:127.0.0.0]/104 [::1]/128
mailbox_size_limit = 0
recipient_delimiter = +
inet_interfaces = all
inet_protocols = all

# Enable SASL authentication
smtp_sasl_auth_enable = yes
# Disallow methods that allow anonymous authentication
smtp_sasl_security_options = noanonymous
# Location of sasl_passwd
smtp_sasl_password_maps = hash:/etc/postfix/sasl/sasl_passwd
# Enable STARTTLS encryption
smtp_tls_security_level = encrypt
# Location of CA certificates
smtp_tls_CAfile = /etc/ssl/certs/ca-certificates.crt

master.cf

master.cf does not need to be modified other than to enable smtpd by uncommenting the following line:

# ==========================================================================
# service type  private unpriv  chroot  wakeup  maxproc command + args
#               (yes)   (yes)   (no)    (never) (100)
# ==========================================================================
smtp      inet  n       -       y       -       -       smtpd

If you require verbose debugging information to get the SMTP connection working, change the line as follows:

smtp      inet  n       -       y       -       -       smtpd y

sasl/sasl_passwd and sasl/sasl_passwd.db

Create the directory /etc/postfix/sasl.

Create the file /etc/postfix/sasl_passwd as follows:

[smtp.gmail.com]:587 username@gmail.com:xxxx xxxx xxxx xxxx

where username is your Gmail account name and xxxx xxxx xxxx xxxx is the App Password Google gave you.

Run: sudo postmap /etc/postfix/sasl_passwd to build the hash file sasl_passwd.db.

Dovecot

The Dovecot POP3 server configuration files are in /etc/dovecot. I had to edit the following two files (starting from the default Raspbian package):

  • /etc/dovecot/conf.d/10-auth.conf
  • /etc/dovecot/conf.d/10-master.conf

Once Dovecot has been configured, the service may be controlled as follows:

  • systemctl start dovecot - start service.
  • systemctl stop dovecot - stop service.
  • systemctl status dovecot - status of service.

10-auth.conf

The only non-comment lines are as follows:

disable_plaintext_auth = no
auth_mechanisms = plain
!include auth-system.conf.ext

10-master.conf

I enabled the POP3 service on port 110 by uncommenting the port = 110 line as follows:

service pop3-login {
  inet_listener pop3 {
    port = 110
  }
  inet_listener pop3s {
    #port = 995
    #ssl = yes
  }
}

Fetchmail

Fetchmail's configuration is in the file /etc/fetchmailrc. It should look like this:

set postmaster "pi"
set bouncemail
set no spambounce
set softbounce
set properties ""
poll imap.gmail.com with proto IMAP auth password
       user 'username' is pi here
       password 'xxxx xxxx xxxx xxxx'
       ssl, sslcertck, idle

Replace the xxxx xxxx xxxx xxxx with the App Password Google gave you. Replace username with your email account name.

Make sure the permissions on the configuration file are okay:

chmod 600 /etc/fetchmailrc
chown fetchmail.root /etc/fetchmailrc

Edit /etc/default/fetchmail to enable the Fetchmail service:

START_DAEMON=yes

Service controls:

  • systemctl start fetchmail - start service.
  • systemctl stop fetchmail - stop service.
  • systemctl status fetchmail - status of service.

Testing

Log messages from all these packages are written to /var/log/mail.log.

You can test the Postfix SMTP server using telnet. Be aware that it may not work the same way from the Pi (ie: localhost) than from a different machine on your LAN, so it is better to connect from another host.

Connect to SMTP like this telnet raspberrypi 25. Typing the following commands should send an email:

HELO myhost.mydomain.com
MAIL FROM:<myaccount@mydomain.com>
RCPT TO:<someotheraccount@somedomain.com>
DATA
Subject: Test message
This is just
a simple test.
.

The final period on its own serves to terminate the message and signal to Postfix that it should process the DATA block and enqueue the message.

Configuring SAM2 Email Client on the GS

Configuring the client is simple:

  • Incoming mail via POP3
    • Hostname: hostname or IP address of your Raspberry Pi
    • Port: Default (110)
    • Username and password: Your Raspberry Pi account credentials
  • Outgoing mail via SMTP
    • Hostname: hostname or IP address of your Raspberry Pi
    • Port: Default (25)
    • Username and password: Your Raspberry Pi account credentials

Bobbi Jun 17, 2020 bobbi.8bit@gmail.com