iOS Push Provider for Courier IMAP

Courier-APNs is a small daemon designed to add Push support to Courier IMAP. Even tough the implementation is kept simplistic it was designed to be scalable.

Features

• Uses APNS/2 and hence supports HTTP/2 connection
• Uses persistent connections to APNs
• Manages expired tokens
• Integration into Courier IMAP has a minimal risk

Caveats

I have Courier-APNs running for several domains without any issues. However my systems handles a couple of hundred emails per day only. The code is not tested in high load situations. Moreover adding Push support to Courier IMAP requires changes to the source code.

Note: Courier-APNs assumes that all mail accounts share a single UID/GID i.e. mail:mail.

Prerequisites

• Google Go
• daemonize
• maildrop
• openbsd-netcat or socat

Install

• Obtain a valid Certificate for the Apple Push Notifications Service. Stefan Arentz has a well written guide. If you don’t own an OS X Server you can try to sign up for a Certificate on Apples Push Certificates Portal.
• Install Courier-APNs

go install github.com/drandreas/courier-apns@latest

• Launch Courier-APNs. It will display your UID. Keep it for later.

$GOPATH/bin/courier-apns /path/to/certificate /path/to/private/key
2016/05/06 19:39:50 Loading certificate...
2016/05/06 19:39:50 UID=com.apple.mail.XServer.647cc087-774a-41ab-b9e5-77fafef13b8e
2016/05/06 19:39:50 Make sure your IMAP_XAPPLEPUSHSERVICE_TOPIC is set accordingly.
2016/05/06 19:39:50 Establishing connection...
2016/05/06 19:39:50 Waiting for request...

• Stop Courier-APNs CTRL-C and re-launch it as daemon:

daemonize -p /var/run/courier/courierapns.pid  \
          -l /var/run/courier/courierapns.lock \
          -u mail  \
          $GOPATH/bin/courier-apns -d \
                     /path/to/certificate \
                     /path/to/private/key

• Patch Courier IMAP with courier-0.75.0-imap.patch, compile and install it.
• Add XAPPLEPUSHSERVICE to IMAP_CAPABILITY in /etc/courier/imapd
• Add IMAP_XAPPLEPUSHSERVICE_TOPIC=YOUR_UID to /etc/courier/imapd
• Resetart Courier IMAP and check if it is advertising XAPPLEPUSHSERVICE

telnet localhost 143
Trying ::1...
Connected to localhost.
Escape character is '^]'.
* OK [CAPABILITY ... XAPPLEPUSHSERVICE ...] Courier-IMAP ready.

• Add push to your mail delivery routine /etc/courier/maildroprc

with netcat:

# Push Notification...
PUSH=`echo $HOME | nc.openbsd -U /var/run/courier/courierapns.socket`
echo $PUSH

with socat:

# Push Notification...
PUSH=`echo $HOME | socat /var/run/courier/courierapns.socket STDIN`
# Note: echo $PUSH will not work with socat

• Reboot your iDevice and manually refresh your Inbox. Push support should now be available in Settings. In rare cases you might need to re-add your mail account to your iDevice for it to recognize push support.

Debugging

• Courier-APNs is verbose. If you run into issues check /var/log/syslog and /var/log/mail.log for hints.
• Courier-APNs stores its data in $Maildir/.push/. For each device a separate file is created e.g.

{
   "aps-version": 2,
   "aps-account-id": "0715A26B-CA09-4730-A419-793000CA982E", 
   "aps-device-token": "2918390218931890821908309283098109381029309829018310983092892829", 
   "mailboxes": [ "INBOX", 
                  "INBOX.Sent"
                ]
}

Command line

courier-apns --help
usage: courier-apns [<flags>] <crt> <key>

Listens to on a Unix socket and performs mail notifications.

This deamon supports persistent connections to APNs. The expected input on the Unix socket
is a single line containing a path to a Maildir. The client can be as simple as a piped echo
e.g. echo /path/to/maildir | nc.openbsd -U /var/run/courier/courierapns.socket.
Flags:
      --help        Show context-sensitive help (also try --help-long and --help-man).
  -s, --socket="/var/run/courier/courierapns.socket"
                    Path to use for Unix socket.
  -d, --syslog      Use Syslog instead of STDERR.
  -c, --concurrent  Enable concurrent request handling.
      --version     Show application version.

Args:
  <crt>  Path to certificate file.
  <key>  Path to private key file.

Sources

• https://github.com/st3fan/dovecot-xaps-daemon
• st3fan/dovecot-xaps-daemon#46
• matthewpowell/pushnotify#1