Update mail configuration to use SSL with custom socket factory.

backend/src/main/resources/application.properties

@@ -16,4 +16,5 @@ spring.mail.port=${MAIL_PORT:465}
 spring.mail.username=${MAIL_USER}
 spring.mail.password=${MAIL_PASSWORD}
 spring.mail.properties.mail.smtp.auth=true
-spring.mail.properties.mail.smtp.starttls.enable=true
+spring.mail.properties.mail.smtp.ssl.enable=true
+spring.mail.properties.mail.smtp.socketFactory.class=javax.net.ssl.SSLSocketFactory