You can create Triggered Emails for Account holders. The email is triggered to fire off of their Birthdate or their Account Creation Date, as a celebration.
This type of Triggered Email is system wide -- it does not need to be assigned to anything. You can have multiple of this type of Triggered Email in your database
Creating the Email Message
Login to the Administrative side of your database, and navigate to Settings --> Assignments --> Email Messages. Click to Add New Email. Input a Title, choose the type Triggered Account, and click the "Save" button.
You can now begin to compose your Email Message. Input a Subject, and add text to the Body. You can use plain text, and you can use Operators. Operators read data from the system that is relevant to the Account, and input that data into the email. After you are finished composing your email message, click the "Save" button.
Creating the Triggered Email
Navigate to Settings --> Assignments --> Triggered Emails. Click the "Add New Triggered Email" button. 
Input a Title, choose the Type, select your Message, choose the date range that the Triggered Email will be used. If you want the Triggered Email to not expire, you can select No End Date.
The trigger is fired off of a date. The types of dates available are Birthdate or their Account Creation Date. Input a day value, indicate before or after, and then select the type of date.
For example, you can send an email to Account holder on their Birthdate, as seen in the screenshot below.