An Outbound message sends information to a specified URL endpoint. Information contains the fields specified at the time of creating an outbound message. It sends a secure, configurable API message(in XML format) to a designated listener.

An Outbound message is a part of Workflow and can be created for a Workflow rule. Whenever an action with Workflow rule is triggered and the rule has outbound message action, then the information specified in the Outbound action will reach to the endpoint URL.

Workflow Rule:

It is used to automate tasks, email alerts, field updates and Outbound messages actions.

Click on Setup --> Create --> Workflow & Approvals --> Workflow Rules

In the new rule, select the object to which you want to define an automated action.

Give the rule name, description and in the evaluation criteria, select the option from the three given criteria.

In rule criteria, select the required pick list value and specify the field, operator and value. Here, we specify the criteria whenever that rule met its requirement then an action should be triggered.

After creating a workflow rule, we will add workflow actions in add workflow action button. In that, select New Outbound message.

Outbound messaging:

Provide name, Endpoint URL(receives the message), user to send as fields.

Select the account fields which you want to send in the Outbound message(whenever workflow rule is triggered and the information which is saved in those fields will be sent as a message to the endpoint URL specified).

The message is delivered in XML format.

In the Outbound messaging monitor section, we can have a look at next items for delivery and oldest failures in a queue.

In those two, we can see outbound message details which we created and their actions such as on which object it was created, number of attempts made to send the message, created date and time, delivery failure reason. 

We can retry or delete the outbound message which is failed to deliver.