The @Resource annotation must be used within a bean class. In your case the annotation defined in EmailSenderService
it is just ignored by the EJB Container.
According to ejb 3.1 specification:
16.4.1.1Injection of Simple Environment Entries Using Annotations.
The Bean Provider uses the Resource annotation to annotate a field or method of the bean class as a target for the injection of a simple environment entry.
Also notice that the field must not be static.
16.2.2Annotations for Environment Entries.
The field or method may have any access qualifier (public, private, etc.) but must not be static.