feat(mail): outbox, SMTP sender and config

pom.xml

@@ -40,6 +40,10 @@
             <groupId>org.springframework.boot</groupId>
             <artifactId>spring-boot-starter-cache</artifactId>
         </dependency>
+        <dependency>
+            <groupId>org.springframework.boot</groupId>
+            <artifactId>spring-boot-starter-mail</artifactId>
+        </dependency>
         <!-- Rest Caching -->
         <dependency>
             <groupId>com.github.ben-manes.caffeine</groupId>