diff --git a/src/mail.js b/src/mail.js
index ff3ce54de..2439f2b0f 100644
--- a/src/mail.js
+++ b/src/mail.js
@@ -1122,7 +1122,7 @@ async function sendTestMail(domain, to) {
     const result = await getDomain(domain);
     if (!result) throw new BoxError(BoxError.NOT_FOUND, 'mail domain not found');
 
-    await mailer.sendTestMail(result.domain);
+    await mailer.sendTestMail(result.domain, to);
 }
 
 async function listMailboxes(domain, search, page, perPage) {
diff --git a/src/mailer.js b/src/mailer.js
index 0632fe19a..69be6d9be 100644
--- a/src/mailer.js
+++ b/src/mailer.js
@@ -61,7 +61,7 @@ async function sendMail(mailOptions) {
         }
     }));
 
-    const transportSendMail = util.promisify(transport.sendMail);
+    const transportSendMail = util.promisify(transport.sendMail).bind(transport);
     const [error] = await safe(transportSendMail(mailOptions));
     if (error) throw new BoxError(BoxError.EXTERNAL_ERROR, error);
     debug(`Email "${mailOptions.subject}" sent to ${mailOptions.to}`);
@@ -210,10 +210,9 @@ async function certificateRenewalError(mailTo, domain, message) {
     await sendMail(mailOptions);
 }
 
-async function sendTestMail(domain, email, callback) {
+async function sendTestMail(domain, email) {
     assert.strictEqual(typeof domain, 'string');
     assert.strictEqual(typeof email, 'string');
-    assert.strictEqual(typeof callback, 'function');
 
     const mailConfig = await getMailConfig();
 
@@ -225,5 +224,5 @@ async function sendTestMail(domain, email, callback) {
         text: render('test.ejs', { cloudronName: mailConfig.cloudronName, format: 'text'})
     };
 
-    await sendMail(mailOptions, callback);
+    await sendMail(mailOptions);
 }