Stellar Data Recovery Knowledge Base (KB) Articles 810

SKB1102

Troubleshooting the ‘Mailbox does not exist’ Error

Problem Description You are unable to start migration jobs or perform actions that require connecting to your Microsoft 365 (Office 365) tenant using Stellar Migrator for Exchange. The software displays one of the following (or similar) error messages: Mailbox does not exist This error prevents successful authentication and migration operations. Root Cause The Microsoft 365 admin account ..

Date Published 19 Dec 2025

Total Views 16

SKB1104

Error: 503 Server Unavailable During Exchange Online (EWS) Migration

A 503 – Server Unavailable error from Exchange Online is one of the most common failures during EWS migrations, and it always means: Exchange/Office 365 is temporarily refusing your connection because of throttling, overload, or mailbox database movement. This is NOT a permanent failure. It is a temporary block. Causes: 1. Throttling (Most Common) Microsoft heavily throttles EWS: • ..

Date Published 19 Dec 2025

Total Views 12

SKB1106

Unable to Connect to the Remote Server Error During EWS Migration

Error Message You may encounter the following error during migration or connection attempts: The request failed. Unable to connect to the remote server. Problem Description This error is a network-level failure that occurs before Exchange Online or EWS processes the request. The connection to the remote Exchange service cannot be established at that moment. This is a temporary issue..

Date Published 19 Dec 2025

Total Views 12

SKB1107

How to Resolve "The SMTP address has no mailbox associated with it" Error?

Cause: The error indicates that the specified folder (usually the primary mailbox) is missing or not accessible. Most often, this happens because the primary mailbox is not available for the affected user account. Resolution: For Exchange Server (On-Premises): kindly check the Primary Mailbox for the user via the Exchange Admin Center (EAC): Steps to check Primary Mailbox in Exc..

Date Published 19 Dec 2025

Total Views 11

SKB1103

How to resolve "Mailbox Database Temporarily Unavailable" Error

The mailbox database is temporarily unavailable., Cannot open mailbox…”with details like: .Server = SN6PR06MB4621.namprd06.prod.outlook.com .mdbGuid = ... .mailboxGuid = ... It means that Exchange Online temporarily locked or offloaded the mailbox database associated with that mailbox. This usually happens due to throttling, load balancing, or too many concurrent connections hitting the mail..

Date Published 19 Dec 2025

Total Views 11

SKB1105

Underlying Connection Was Closed Error During EWS Migration

Error Message During migration or mailbox processing, you may see the following error: The request failed. The underlying connection was closed: An unexpected error occurred on a send. Problem Description This error is a network-level failure that commonly occurs during EWS migrations, especially when migrating a large number of items or large mailbox data. The connection between the migratio..

Date Published 19 Dec 2025

Total Views 9