550 5.1.1 Recipient address rejected: User unknown in virtual mailbox table

Products

• Email Security.cloud

Issue/Introduction

Email is not delivered and bounced back with error: 550 5.1.1 Recipient address rejected: User unknown in virtual mailbox table

Environment

Email security cloud

Cause

The error informs the sender about the fact that such a mailbox has not been found.

Resolution

If the recipient address is correct, it is necessary to contact the recipient and inform him about the delivery rejection. The rejection isn't caused by Email security cloud but by recipient security application or mail server provider.