Introduction to EMail Push in Open-Xchange

Abstract

In combination with OXtender_for_Business_Mobility (EAS) and OXtender_2_for_Microsoft_Outlook (OLOX2) a working mail push is very important. It is important to know, that this is a combined requirement to the mail server and the Open-Xchange server to make that happen.

Both of the listed OXtenders are accessing Open-Xchange via the USM interface (Universal Synchronization Module, which is the package open-xchange-usm).

In summary:

  • EAS uses an internal mail poll if no push available
  • OLOX2 is depending on an external mail push trigger

Mail Push with OXtender_for_Business_Mobility

In addition to an externally triggered mail push, in internal mail poll initiated by the usm module is executed.

This is, how this polling can be influenced via /opt/open-xchange/etc/groupware/usm.properties:

  1. com.openexchange.usm.session.sync.email_pull_delay=50%
  2. com.openexchange.usm.session.sync.email_pull_min_delay=60000


These values are the default values.

1. defines, when an internal poll should be triggered while waiting for the client. This can be done as an absolute value (in milliseconds) or as a percentage value based on the waiting time as been specified by by the client per Active Sync Protocol (EAS). In the EAS protocol, the client specifies this time dynamically, usually between 30 seconds and 30 minutes. If an absolute time is specified here and the time set by the client is smaller, a mail poll is initiated at the end of the waiting time if not prevented by the setting of 2.


2. defines an additional minimum waiting time, which is enforced to be followed, before an internal poll is executed. Is the value as specified by the EAS client/protocol smaller than this value, no poll will be executed. If 2. is set to a negative value, the internal mail polling of USM will be completely disabled.


Examples

A

com.openexchange.usm.session.sync.email_pull_delay=50%
com.openexchange.usm.session.sync.email_pull_min_delay=-1

Internal mail poll is disabled.

B

com.openexchange.usm.session.sync.email_pull_delay=50%
com.openexchange.usm.session.sync.email_pull_min_delay=60000


Client waiting time Mail polling interval
30 seconds no polling
90 seconds poll after 60 seconds (!)
180 seconds poll after 90 seconds
1800 seconds poll after 900 seconds

C

com.openexchange.usm.session.sync.email_pull_delay=120000
com.openexchange.usm.session.sync.email_pull_min_delay=60000
Client waiting time Mail polling interval
30 seconds no polling
90 seconds poll after 90 seconds (!)
180 seconds poll after 120 seconds
1800 seconds poll after 120 seconds


D

com.openexchange.usm.session.sync.email_pull_delay=60000
com.openexchange.usm.session.sync.email_pull_min_delay=120000
Client waiting time Mail polling interval
30 seconds no polling
90 seconds no polling (!)
180 seconds poll after 120 seconds
1800 seconds poll after 120 seconds


This example is not usefull, it should show, that property 2. has a higher priority than property 1.


The default behaviour can be described like shown below:

client waiting time X (EAS Ping):
        X < 60 s   -> no internal mail poll
60 s <= X <= 120 s -> internal poll after 60 s
120 s < X          -> internal poll after X/2 s

Mail Push with OXtender_2_for_Microsoft_Outlook

In OLOX2 USM does NO internal mail poll at all. There are no long running waiting requests (like with Ping in EAS). Instead, the client (Outlook OXtender) does http requests in short intervals asking for changes. This is the reason why USM does no internal mail poll but is depending on messages from the Open-Xchange server (using OSGi Events). The only exception is, when the client changes from one email folder to another one. This will initiate a sync.

Open-Xchange Mail Push implementations

There are currently two publicly available implementations of mail push.

The MailNotify_Bundle

This package only integrates with cyrus-imapd at the moment. We prepared a plugin for dovecot2, but it's not part of the official upstream tarball. Please contact us if you are interested in it.

The MALPoll Bundle

The package open-xchange-push-malpoll simulates mail push in polling the imap server on a regular basis. This can only be recommended on small installations as it might stress the imap server.

The MailPushIMAPIDLE Bundle‎

New since latest 6.20 update!

Mail push via IMAP IDLE. Works with all imap servers being able to do IMAP IDLE.