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vagifazari's avatar
vagifazari
Copper Contributor
Jul 09, 2024

Exchange 2016 ERROR - The following recipient(s) cannot be reached:

Hi everyone,   Over the last 2-3 months, we have been experiencing issues with sending and sometimes receiving emails from both internal and external organizations.   Error message: (When our use...
2016
admin
Exchange Server
GuidovanDijk's avatar
GuidovanDijk
MCT
Jul 05, 2025

Hi ​,

Possible root cause based on your error
a corrupted mailbox item or issues with the mailbox database, typically affecting Conversation View aggregation.

Causes:

  • Corrupt mailbox item or folder (e.g. Conversation index)
  • Database index corruption
  • Issues with the mailbox move history or tombstoned folders
  • Third-party add-ins or antivirus scanning mailbox data

Actions:

  1. Identify if it's user-specific
    Check if this error only occurs for:

A single user
Multiple users on the same mailbox database

If it’s user-specific, proceed to mailbox repair (step 2). If multiple users are affected, investigate the database and server-level issues.

  1. Run a mailbox repair (ISInteg style)
    Use New-MailboxRepairRequest on the affected user’s mailbox:
New-MailboxRepairRequest -Mailbox "username" -CorruptionType ProvisionedFolder,SearchFolder,AggregateCounts,FolderView

You can monitor the repair progress in the Event Viewer (Application log, source: MSExchangeIS).

  1. Check if it's reproducible
    Ask the user to try:
    • Forwarding the email
    • Rewriting it from scratch
    • Sending without attachment

If one of these works, the item is likely corrupted

  1. Move the mailbox to a new database
    If mailbox repair fails or error persists:
New-MoveRequest -Identity "username" -TargetDatabase "NewDatabaseName"

A mailbox move can purge corrupt folders/items that cause MAPI-level errors.

  1. Check Event Logs
    On the Exchange server(s), look in:
    • Application logs (for MSExchangeIS and MSExchangeTransport)
    • System logs (hardware or disk issues)

          Check for recurring 1108 or MAPI errors.

 

WorkAround

Disable Conversation View (workaround)
Temporarily disable conversation processing for the mailbox as a test :

Set-Mailbox <username> -MessageCopyForSentAsEnabled $false
Set-Mailbox <username> -MessageCopyForSendOnBehalfEnabled $false

Or disable it in Outlook to avoid the problematic agent (not a fix, but a workaround).

 

if it’s still unsolved:

  • Use MFCMAPI tool to inspect the problematic message/folder
  • Export the message to PST and reimport after scan
  • Open a Microsoft support case if multiple users are impacted
    NOTE Exchange 2016 is end of extended support as of oktober 14, 2025

Regards

 

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