How to Set Auto-Replies for Shared Mailboxes with PowerShell

Tell External People that the Company’s on Holiday

The question arose about the best way to set auto-reply for a shared mailbox to inform external senders that the company is on holiday (public or otherwise). Some suggested using Flow for the job. I, of course, thought of PowerShell. I’m not against Flow: I simply think that PowerShell offers more control and flexibility, especially when multiple shared mailboxes are involved. For instance, you might want to set appropriate auto-reply messages up for all the shared mailboxes in an organization, especially if those mailboxes are used for customer interaction.

Auto-replies, or OOF (Out of Facility) notifications as they are known in the trade, go back to the dawn of email (before Exchange 4.0). Even Teams supports out of office notifications. For Exchange (on-premises and online), it’s easy to manage auto-replies with PowerShell using the Set-MailboxAutoReplyConfiguration cmdlet. The Get-MailboxAutoReplyConfiguration cmdlet reports the current auto-reply state of a mailbox. You can have separate auto-reply messages for internal (any mail-enabled object within the organization) and external senders (anyone else).

A New Auto-Reply for Shared Mailboxes

The example solution uses a quick and dirty script to find all shared mailboxes in the tenant and set two auto-replies on each mailbox. One (brief) for internal correspondents; the other (less terse and nicer) for external people. Two variables are declared to set the start and end time for the scheduled auto-reply. If you specify a time, remember that Exchange Online runs on UTC so any time you set is in UTC. In other words, you should convert your local time to UTC when you set up the auto-reply. Rather bizarrely, Get-MailboxAutoReplyConfiguration converts the UTC time to local (workstation) time when it reports an auto-reply configuration.

#These times are in UTC
 $HolidayStart = "04-Aug-2019 17:00"
 $HolidayEnd = "6-Aug-2019 09:00"
 $InternalMessage = "Expect delays in answering messages to this mailbox due to the holiday between <b>" + $HolidayStart + "</b> and <b>" + $HolidayEnd + "</b>"
 $ExternalMessage = "Thank you for your email. Your communication is important to us, but please be aware that some delay will occur in answering messages to this mailbox due to the public holiday between <b>" + $HolidayStart + "</b> and <b>" + $HolidayEnd + "</b>"
 [array]$Mbx = (Get-ExoMailbox -RecipientTypeDetails SharedMailbox | Select DisplayName, Alias, DistinguishedName)
    ForEach ($M in $Mbx) {
    # Set auto reply
    Write-Host "Setting auto-reply for shared mailbox:" $M.DisplayName
    Set-MailboxAutoReplyConfiguration -Identity $M.DistinguishedName -StartTime $HolidayStart -AutoReplyState "Scheduled" -EndTime $HolidayEnd -InternalMessage $InternalMessage –ExternalMessage  $ExternalMessage -ExternalAudience 'All' -CreateOOFEvent:$True }

The code above uses the Get-ExoMailbox cmdlet from the Exchange Online management module, which is what you should use in Exchange Online. However, the Get-Mailbox cmdlet will work, and it’s what you use for Exchange on-premises.

Figure 1 shows the result when an external person sends an email to a shared mailbox. You can be as creative as you like with the text when you set the auto-reply on the mailbox. Because Exchange stores the auto-reply message in HTML format, most basic HTML formatting commands work when you set auto-reply for a shared mailbox. I only use bolded text in this example, but you could also include something like a mailto: link to tell people who they should contact if someone is out of the office and unavailable.

Removing Auto-Replies

The scheduled auto-reply lapses when the end time arrives. If you want to remove the auto-replies from all shared mailboxes, run the command:

# We assume that all shared mailboxes are in $Mbx
 ForEach ($M in $Mbx) {
   Set-MailboxAutoReplyConfiguration -Identity $M.DistinguishedName  -AutoReplyState "Disabled" }

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For more information about working with shared mailboxes, see the Exchange Online chapter in the Office 365 for IT Pros eBook. There’s over a thousand PowerShell examples in the book, including lots of examples of using PowerShell to work with the Microsoft Graph.