The following article refers to functionality available in Workflow builder, which can be accessed in one of the following locations, depending on your configuration:

Administration -> HR -> Workflows 
or
Administration -> HR -> Workflows -> Workflows

Within a workflow, it is possible to trigger emails at a set period before, on or after an employee work anniversary or birthday, when doing this you should use build separate workflows for anniversary and birthday reminders to save confusion when they are triggered.  Workflows of this type can be used to prearrange actions around employee anniversaries or birthdays and to notify necessary parties of this key information.  For example, an employee's manager might want to be notified of their team's birthdays so they can arrange a birthday card from their team!

In order to set up a workflow of this type to run continuously, the workflow options to select are:

1. Category - Continuous
2. Type - Trigger Date

This type of workflow will trigger based on the "When should this happen?" condition in the first workflow step.  For example, using the following "When should this happen?" condition in the first step  will cause the workflow to trigger 1 week before the employee's birthday:
 

Similarly, the following "When should this happen?" condition in the first step will cause the workflow to trigger 1 week before the employee's work anniversary:



You can also use "system fields" to include relevant information in the workflow email.

For example the [employee_next_age] system field can be used to get the employee's age at their next birthday and [employee_birthday_date] to get the date of their birthday. The below example is a workflow email sent to the employee's manager which includes the name of the employee in the subject and information about the employee's current manager and the employee in the email.

The step is set up in the workflow as follows:

This would produce a result like below:

System fields which can be used to relate to a work anniversary include:

•  [employee_anniversary_date] - Gives the next work anniversary date for the employee formatted as DD/MM/YYYY
• [employee_service_years] - Gives the employees current years service as a numerical value
• [employee_next_service_years] - Gives the employees next years service as a numerical value

It is also possible to set up work anniversary notifications without using a custom workflow, for further details click here.