#204: Log exception for failing threads

Author: bbottema

Diff for: src/main/java/org/simplejavamail/mailer/internal/mailsender/MailSender.java

@@ -200,7 +200,11 @@ the proxy bridge server (or connection pool in async mode) while a non-async ema
 			executor.execute(new NamedRunnable("sendMail process") {
 				@Override
 				public void run() {
-					sendMailClosure(session, email);
+					try {
+						sendMailClosure(session, email);
+					} catch (Exception e) {
+						LOGGER.error("Failed to send email", e);
+					}
 				}
 			});
 		} else {