Send a start registration window email to a set of mail addresses

[dominikhorn93]

Description

When the registration window starts, an email is sent to all students. This is done via service task in camunda.

Tasks

• define the mail text in code
• define the mail addresses in application.properties
  • inject them via @Value into a property in your mailService
• add mail functionality to the backend (spring mail)
  • mail package with MailService class
  • use a gmail mail adress
• implement a JavaDelegate that calls the MailService
• adjust the bpmn process an the unit test

[VladKay]

I implemented the Properties part without "@Value" annotation, because it was the most optimal solution in this case. I need feedback of my code in "mailingBranch", because it was already done