Error: "Unable to log on to Mailbox" (4318847)

While running the Exchange Mailbox Content and Attachments gathering you get the error "Unable to log on to Mailbox."

Full Error:

Unable to logon to mailbox /O=ORGNAME/OU=EXCHANGE ADMINISTRATIVE GROUP (FYDIBOHF23SPDLT)/CN=RECIPIENTS/CN=USER NAME. 0x8004011D: The Microsoft Exchange Server computer is not available. Either there are network problems or the Microsoft Exchange Server computer is down for maintenance. MAPI_E_FAILONEPROVIDER (Microsoft Exchange Server Information Store) Low level error: 0x0

The Service account does not have Full Mailbox Access to the specific mailbox or to all mailboxes from which you want to gather the content and attachment information.

Exchange 2000/2003

You can grant Full Mailbox Access using Active Directory Users and Computers (ADUC) for a single
mailbox, or you can use Exchange System Manager (ESM) for all mailboxes.

To grant Full Mailbox Access to a specific mailbox using ADUC:

1. Open the ADUC MMC snap-in (console)
2. Open the Properties for the Active Directory Object associated with the mailbox
   from which you want to gather
3. Select the Exchange Advanced tab and click Mailbox Rights
4. Click Add and select the account used to run the Content and Attachments gathering
5. Add Full Mailbox Access permission

To grant Full Mailbox Access to all mailboxes using ESM:

1. Open the properties for an Exchange server using Exchange System Manager
2. Select the Security Tab
3. Grant Send As and Receive As permissions to the account used to run the Content and
   Attachments gathering.
    

Exchange 2007

To grant Full Mailbox Access to a specific mailbox using PowerShell:

1. Open the Exchange Management Shell
2. Run the Add-MailboxPermission command. For example, if the mailbox is called My Mailbox and the account is called Trusted User, the
   command would be:
   - Add-MailboxPermission My Mailbox -User Trusted User -AccessRights FullAccess

To grant Full Mailbox Access to all mailboxes using PowerShell:

1. Open the Exchange Management shell
2. Use the Add-ADPermission command to grant the Send-As and Receive-As permissions. For example, if the server is called MyServerr and the account is called Trusted User, the commands would be as follows:
   - Get-MailboxServer MyServer | Add-ADPermission -User Trusted User -ExtendedRights Send-As
   - Get-MailboxServer MyServer | Add-ADPermission -User Trusted User -ExtendedRights Receive-As

Exchange 2010

To grant Full Mailbox Access to a specific mailbox in Exchange 2010:

1. Open the Exchange 2010 Management Shell
2. Run the Add-MailboxPermission command. For example, if the mailbox is called mailboxName and the account is called userName, the command would be:
   - Add-MailboxPermission -id:mailboxName -User:userName -AccessRights FullAccess

To grant Full Mailbox Access to a specific mailbox database in Exchange 2010:

1. Open the Exchange 2010 Management Shell
2. Run the Add-MailboxPermission command. For example, if the mailbox database is called DatabaseName and the account is called userName, the command would be:
   - Get-MailboxDatabase Databasename | Add-ADPermission -User "userName" -ExtendedRights Send-As, Receive-As

To grant Full Mailbox Access to the entire server in Exchange 2010:

1. Open the Exchange 2010 Management Shell
2. Use the Add-ADPermission command to grant the Send-As and Receive-As permissions. For example, if the server is called MyServer and the account is called UserA, the commands are as follows:
   - Get-MailboxServer Myserver | Get-MailboxDatabase | Add-ADPermission -User "UserA" -ExtendedRights Send-As, Receive-As

Note: Make sure that the user account that is used is not a member of the "Domain Admins" group in Active Directory.
If it is remove the "Domain Admins" group from the service account. Remove the Full Access permissions, apply the changes then add the Full Access Permissions back.