Since the release of Lotus Domino Server 8.0.1, Domino has natively supported wireless synchronisation of mail and calendar PIM data with devices running Windows Mobile 5 or later via Lotus Traveler, or Lotus iNotes as it has now been renamed, without the need for any third party software or middleware.
Lotus Traveler is a separate component not included in the standard installation of Domino Server, and must be installed separately.
The installation procedure is simply a matter of running an executable and specifying the target folder for the program files to be extracted to. Once installed the Domino server will need to be rebooted.
Configuration
The Traveler installation wizard should have set all of the required settings automatically. Should you wish to verify the settings governing Traveler, look at the following:
Launch the Domino Administrator client.
Browse to Configuration --> Server --> Current Server Document --> Basics
Set the option to Load Internet Configurations From Server/Internet Sites to Enabled:

Browse to Internet Protocols
Select the HTTP tab
Set the Maximum Requests Per Persistent Connection to at least 100
Set the Input Timeout to at least 75 seconds

Save the changes
Browse to Web --> Internet Sites
The Traveler installation should have created a new web site automatically.

Verify that the host name field is correctly set to the external name (FDQN) of the Domino server. If the server is to be accessed locally via the LAN and has a different internal name from the external one, add this name also.
Click on the Domino Web Engine tab
Set Session Authentication to Single Server
Click on the Security tab
If you want to allow only TCP connections, set the following:
If you want to allow only SSL connections, set the following (this assumes that the correct SSL certificate configuration has already been applied to the Domino server):
If you want to allow both SSL and TCP connections, set the following:

Save the changes
Restart the HTTP Server by browsing to Server --> Status --> Server Tasks --> HTTP Server and selecting Restart:

IMPORTANT
(this foxed me initially)
If you did not have any web sites configured on the server prior to the Lotus Taveler installation, the web site created for Traveler will be configured with a default web site rule of ‘override session authentication’.
If the Domino server that Traveller has been installed on is also the messaging server, this will effectively turn off authentication on the SMTP server service and will cause the SMTP server to stop accepting mail.

One solution is to create a separate Inbound SMTP queue:

And then restart both the HTTP and SMTP server tasks. This resolved the issue for me, but I don't know if there is a better way of doing it. If there are any Domino experts reading this, let me know if there is!
Usage
The Traveler client can now be downloaded to the Windows Mobile 5/6 device by opening a web browser on the client device and browsing to the address of the Domino server:

Select the version of Windows Mobile you are using. If the multilingual version of Traveler was installed, you will be prompted to select the desired language:

Once downloaded, run the CAB file. The following window will be displayed:

Tap Next, the following window will be displayed:

Enter your username and password and the external FQDN or IP address of the Domino Traveler server. These are the only settings that must be entered. Tapping on the Advanced button allows you to edit the connection settings:

If you are unsure about what settings to use, leave them at the default values.
By default the Traveler client communicates with the Traveler server via TCP port 8642 to send polling commands. This port can be changed by the administrator by browsing to Configuration --> Web --> Web Server Configuration --> Lotus Traveler --> AutoSync Settings
Tap Next, the following window will be displayed:

Select which mailbox folders you wish to synchronise with the client. Tap Next and then Finish:

The Lotus Traveler application will now be listed in the Programs folder, and a new folder will also have been created within the Messaging application:

To edit the default synchronisation settings, tap on the icon for the Traveler application and select Menu --> Settings:

The Account settings allow you to adjust the username, password and server address entered during the initial configuration:

The Mail and Calendar settings allow you to configure how far back into the past you synchronise, and the amount of data to retrieve:

The Other Applications settings allow you to specify how you want to synchronise the other mailbox folders: Contacts, Notes and Tasks:

The Auto Sync settings allow you to specify whether you wish to synchronise via a TCP connection, or have the server send you a ‘wake-up’ SMS message to trigger a synchronisation:

The Server Settings option displays the same information as that in the Advanced section of the initial setup and allows you to adjust the ports used to connect to the Traveler server:

The Logging settings allow you to set the level of detail the log file should go into, and also set a maximum log file size:

Your device is now configured for Lotus Notes Traveler.

Links:
[1] http://ukblog.im-mobility.com/category/blog/domino
[2] http://ukblog.im-mobility.com/category/blog/ibm
[3] http://ukblog.im-mobility.com/category/blog/lotus
[4] http://ukblog.im-mobility.com/category/blog/lotus-domino
[5] http://ukblog.im-mobility.com/category/blog/lotus-notes
[6] http://ukblog.im-mobility.com/category/blog/lotus-traveler