diff --git a/src/routes/apps.js b/src/routes/apps.js
index 1c3dee1b4..8161658a1 100644
--- a/src/routes/apps.js
+++ b/src/routes/apps.js
@@ -373,7 +373,7 @@ async function setMailbox(req, res, next) {
     if (req.body.enable) {
         if (req.body.mailboxName !== null && typeof req.body.mailboxName !== 'string') return next(new HttpError(400, 'mailboxName must be a string'));
         if (typeof req.body.mailboxDomain !== 'string') return next(new HttpError(400, 'mailboxDomain must be a string'));
-        if (typeof req.body.mailboxDisplayName !== 'string') return next(new HttpError(400, 'mailboxDisplayName must be a string'));
+        if ('mailboxDisplayName' in req.body && typeof req.body.mailboxDisplayName !== 'string') return next(new HttpError(400, 'mailboxDisplayName must be a string'));
     }
 
     const [error, result] = await safe(apps.setMailbox(req.app, req.body, AuditSource.fromRequest(req)));