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Three ways to handle a disabled mailbox in Exchange

Admins have some options if they want to create messages for disabled email accounts to let senders know the address is no longer in use.

When end users are terminated or leave an organization, it's common to disable their accounts for security reasons....

In many cases, mail continues to go to the mailbox without notifying the senders -- even after the account is deleted. However, there are a few ways to inform email senders that the disabled mailbox is no longer in use or available.

How you do this depends on whether you want to receive mail or reject mail, preserve mailbox content or remove mailbox content from the servers. Here's a look at each option -- an out of office message, a shared mailbox and a transport rule.

Out of Office messages. To keep the disabled mailbox and its content on the Exchange Server, an automatic reply -- also known as an "Out of Office message" -- could work. Setting this up requires the following:

  1. Disable the user account in Active Directory (AD).
  2. Add Full Mailbox permissions to an administrative account.
  3. Sign in to Outlook Web App (OWA) as an administrator account and open the disabled user's mailbox.
  4. Navigate to Options and select Organize E-Mail.
  5. Configure Automatic Replies.

Shared mailboxes. If you want to keep the new mail sent to this recipient for review but not the user's mailbox content, you can associate the email address of this recipient with another mailbox. For example, create a shared mailbox for the sole purpose of announcing the email addresses are no longer in use. One drawback to this option is that the email sending the automatic reply would be different. But this option would work for any number of retired email addresses.

Shared mailboxes also have disabled users accounts, so they aren't a potential security issue. In Exchange 2010, the process to create a shared mailbox is done from the Exchange Management Shell (EMS). In Exchange 2013, it can be done from the EMS and the Exchange Admin Center. Implementing this option requires the following:

  1. Disable the user's account in AD.
  2. Disable the user's mailbox in Exchange.
  3. Create a shared mailbox. For example:
    New-Mailbox NotInUse –Shared –UserPrincipalName [email protected]
  4. Add full mailbox permissions to an administrative account.
  5. Add the email address of the disabled mailbox to the email addresses of the shared mailbox.
  6. Sign in to OWA as an administrator account and open the shared mailbox.
  7. Navigate to Options and select Organize E-Mail.
  8. Configure Automatic Replies.

Transport rules. If we don't want the disabled mailbox to receive any new email, a transport rule may be the best option. Transport rules are stored in AD and all transport services in the organization use them. One rule could be used for a number of retired email addresses. The EMC or the EMS can create the rule. For example:

New-TransportRule –Name "Mailbox not use" –Comments "" –Priority '0' –Enalbed $True –SentTo '[email protected]' –RejectMessageReasonText "This Mailbox is no longer in use" –RegectMessageEnhancedStatusCode '5.7.1'

It's important to note that all of these options require that the email address of the recipient in question is resolvable in the Exchange organization. If the mailbox gets disabled and the email address isn't associated with another mailbox, inbound SMTP connections will be rejected when there is no match for the RCPT TO: command. This message is a not so subtle, and not too friendly, indication that the mailbox isn't in use anymore:

#< #5.1.1 smtp;550 5.1.1 RESOLVER.ADR.RecipNotFound; not found> #SMTP#

About the author: 
Richard Luckett is a consultant and instructor specializing in messaging and unified communications. He's been a certified professional with Microsoft since 1996 and has 20 years of experience in the public and private sectors. He's a Microsoft Certified Trainer with more than 15 years of training experience with the Microsoft product line and received the Exchange MVP award in 2006, 2007 and 2008. He's also an expert in deploying and integrating Exchange Server and Lync Server. He leads the Microsoft training and consulting practice at LITSG.

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