mailer: log error and do not throw

this suppresses eventlog exceptions when mail is down or the
mail is rejected because outbound is disabled.

in apphealthmonitor, we hit a case where eventlog entries are
continuously added since mailer was not sending emails. the health
state of the app is never switched because mail sending failed.

src/mailer.js

@@ -66,12 +66,14 @@ async function sendMail(mailOptions) {
         auth: {
             user: mailOptions.authUser || `no-reply@${dashboardDomain}`,
             pass: data.relayToken
-        }
+        },
+        logger: false,
+        debug: false // set to true for smtp logs
     });
 
     const [error] = await safe(transport.sendMail(mailOptions));
-    if (error) throw new BoxError(BoxError.EXTERNAL_ERROR, error);
-    debug(`Email "${mailOptions.subject}" sent to ${mailOptions.to}`);
+    if (error) debug(`Error sending Email "${mailOptions.subject}" to ${mailOptions.to}: ${error.message}`);
+    else debug(`Email "${mailOptions.subject}" sent to ${mailOptions.to}`);
 }
 
 function render(templateFile, params, translationAssets) {