MailServiceImpl.sendMail(): add comment.

No code changes.

Author: php-coder

src/main/java/ru/mystamps/web/service/MailServiceImpl.java

@@ -122,6 +122,8 @@ private void sendMail(
 		final String tag) {
 
 		try {
+			// We're using MimeMessagePreparator only because of its capability of adding headers.
+			// Otherwise we would use SimpleMailMessage class.
 			MimeMessagePreparator preparator = new MimeMessagePreparator() {
 				@Override
 				@SuppressWarnings("PMD.SignatureDeclareThrowsException")