[SalesForce] outbound messages limit

You can't control this, the background delivery process will deliver whatever is ready the next time it checks, although it is unusual to not get bunched notifications when you update multiple rows in a single transaction.

As you have found, the outbound message callout isn't able to pass the current session ID in the format required for the Salesforce hosted web service.

The SessionId this is passed is a parameter rather than a header as required by the webService keyword.

Instead, you can host the Apex web service in a public Force.com Sites instance. This would bypass the need for the Session ID header. Add the class containing the webservice to the Public Access Settings for the Site.

If you want, you could use a separate web service for the site that uses the SessionId from the request to call the secured web service. However, by this stage things are getting a bit ugly with the request bouncing along from outbound message to Sites web service to secured web service.

See also:

• Exposing Apex Web Service class via Force.com Sites
• SOAP request to APEX webservice without requiring authentication?