Exchange Online Automatic Replies: Out-of-Office Setup, Audience Settings, PowerShell, and Leaver Handling

Everyone knows how to turn on an out-of-office message. Few organizations have a standard for what it says, who can see it, or how it is handled when a person leaves. This guide fills those gaps.

How Automatic Replies Work

An automatic reply is stored in the mailbox and sent by Exchange Online, so it works even when Outlook is closed. Key behaviors:

• One reply per sender per period. Exchange sends one reply to a given sender each time the setting is turned on. It does not reply to every message from the same person.
• Two audiences. An internal message (people in your organization) and an external message (everyone else, or only known contacts).
• Scheduled or immediate. Replies can be on, off, or scheduled with start and end times.
• Not sent to everything. Exchange does not reply to mailing lists, bulk mail, junk mail, or messages that are themselves automatic replies, to avoid loops.
• Calendar link. Marking time as Out of office in the calendar can trigger the reply in some clients, but the rule belongs to the automatic reply setting. Check that both agree.

What Users Do

Outlook on the web and new Outlook. Open Settings, Mail, Automatic replies. Turn on Automatic replies, tick Send replies only during a time period, set the start and end, write the message, and decide whether to send replies outside the organization and to whom. Save.

Outlook for Windows (classic). Open File, Info, Automatic Replies. Choose Send automatic replies, tick Only send during this time range, set the times, and write the *Inside My Organization* and *Outside My Organization* tabs.

Mobile. In the Outlook app, open Settings, choose the account, then Automatic replies.

Tips for good replies.

1. State the return date (or the date they will be reachable).
2. Give an alternative contact with an email and, if suitable, a phone number.
3. Say what to do for urgent matters.
4. Keep the external message short and neutral. Do not say "I am on a beach in Spain until the 14th and my house is empty." Do not list travel details, personal circumstances, or that the person is away from the office more than needed.
5. Mention the expected response time if you will check mail occasionally.
6. Use plain text or simple formatting; some clients render rich HTML poorly.
7. Always end it. Forgotten replies that are still active months later are a common embarrassment.

Example internal: "I'm out of the office until 4 January with limited access to email. For urgent matters contact Alex Smith (asmith@contoso.com). Otherwise I will reply when I return."

Example external: "Thank you for your message. I am away from the office until 4 January. For urgent matters please contact support@contoso.com."

Internal, External, and Known Contacts

The external audience setting is the key security decision.

Setting	Who receives the reply
None	Only internal senders get a reply
Known	External senders who are in the user's Contacts get a reply
All	Every external sender gets a reply

Why it matters:

• A reply to an unknown external sender confirms the mailbox is active, which helps spammers and phishers build target lists.
• A reply also reveals when a person is away, which helps social engineering ("The CFO is away until the 14th, so urgent payment instructions will not be questioned").
• A reply to customers can be good service. Use All for shared and role mailboxes, and Known or None for individuals.

A sensible default is Known for staff, All for support and sales mailboxes, and None for executives and finance. Organizations can also manage which kinds of automatic messages may leave the organization by remote domain settings (see below).

What Admins Do (PowerShell)

Notes:

• AutoReplyState can be Disabled, Enabled, or Scheduled.
• Times are interpreted in the mailbox's time zone settings; check that the time zone is correct, or a reply can switch on or off at the wrong hour.
• Messages can contain HTML. Escape quotes and special characters, or build the message from a here-string.
• You can set replies for shared mailboxes and for leaver mailboxes this way.
• To handle many mailboxes, loop over a CSV:

An admin needs the right role, and should keep a record when setting a reply for someone else. Setting a reply is changing a user's communications.

Leavers and Shared Mailboxes

Automatic replies are a standard part of offboarding:

1. Convert the leaver's mailbox to a shared mailbox if the mail must be kept and read (see shared mailboxes and leavers).
2. Set an enabled reply with no end date: "Alex no longer works at Contoso. Please contact support@contoso.com."
3. Set the external audience to All for the leaver's mailbox so customers learn who to contact.
4. Review the message after 3 to 6 months and remove the mailbox or replace the reply with forwarding to a shared address.
5. If the person's address was a public contact, consider an alias on a shared mailbox instead of a reply.

For team addresses, a reply that sets response-time expectations ("We reply within one business day") reduces repeat emails and complaints.

Organization-Wide Controls (Remote Domains)

Exchange Online controls what automatic messages are allowed to leave through remote domains: Exchange admin center, Mail flow, Remote domains. The default remote domain (*) decides, for all external domains:

• Whether automatic replies are allowed.
• Whether automatic forwarding is allowed.
• Whether delivery reports and non-delivery reports go out.
• Whether out-of-office replies are sent as internal-style or external-style messages.
• Whether TNEF conversion is applied.

AllowedOOFType values include External (the normal choice), InternalLegacy, and ExternalLegacy. Use the default unless you have a reason. To stop automatic replies leaving the organization entirely, set AutoReplyEnabled to $false for the default remote domain. That is blunt: it stops all automatic replies to external senders, including useful ones. Use it only for organizations with a strict reason.

You can also create a remote domain entry for a partner to behave differently from the rest of the internet.

Loops, Lists, and Other Pitfalls

• Auto-reply loops. Two mailboxes with automatic replies can reply to each other. Exchange prevents most loops by sending only one reply per sender and ignoring messages marked as automatic. Be careful with custom rules that reply to everything.
• Distribution lists. A reply to a message sent to a list goes to the original sender, not the list, but a user who is a member of a large list can still send one reply to each sender. A reply storm is unlikely, but members of a very large list can spam the sender. Some organizations use -SendOofMessageToOriginatorEnabled on the group to control this behavior. See distribution groups.
• Mailing list software and bulk mail do not get replies.
• Delegates. Meeting requests handled by a delegate may still prompt a reply for the owner. Review delegates when you set a reply for an executive.
• Forwarding and automatic replies together. A forwarded copy does not trigger a reply from the forwarding recipient unless that recipient also has one.
• Shared mailbox replies and the sender. If a shared mailbox replies automatically, the message comes from the shared address, not from a person.
• Rich content. Large images and tracking-style content in an automatic reply can trigger spam filters at the recipient's end.
• Time zones. A reply scheduled for midnight can go out at the wrong time for a traveler. Use business hours.
• Reply content and disclosure. If your organization is regulated, check whether replies must carry a disclaimer. Some do, and a mail flow rule can add it.

Replies, Rules, and Calendar Status

Need	Use
Tell senders you are away	Automatic reply
Redirect mail while away	Inbox rule or forwarding (mind external-forward blocks)
Show you are away to colleagues	Calendar status Out of office plus automatic reply
Keep a team informed	Shared calendar or team status
Respond differently to specific senders	Inbox rule with *reply using a template* (use carefully)
Notify external senders after leaving the company	Reply on the converted mailbox, then forwarding

See inbox rules for the details on rules that reply or forward and for the security caution about forwarding.

A Simple Standard for the Organization

Publish a one-page standard:

1. Staff set an automatic reply for any absence over one working day.
2. Include the return date and a named alternative contact.
3. The external audience is Known unless the mailbox is a team or support address.
4. Do not include travel details or personal information.
5. Managers check that replies are turned off when staff return.
6. IT sets replies on leaver mailboxes and keeps them for a defined period.
7. IT keeps a template for leaver messages in one place.

How to Check It Worked

• Send a test message from an internal account and confirm you get the internal reply.
• Send from an external account (a personal mailbox) and confirm the external audience behaves as set. Remember that Exchange sends only one reply per sender per period, so test with a fresh sender or toggle the setting.
• Confirm the start and end times by reading back Get-MailboxAutoReplyConfiguration.
• Check the reply switches off at the end time.
• Test a leaver mailbox with All audience.
• Confirm no reply goes to mailing lists or bulk senders.

Troubleshooting

Symptom	Likely cause
External senders get no reply	External audience is None or Known and the sender is not a contact, or the remote domain disables automatic replies
Internal reply works, external does not	The "outside my organization" option is off, or AutoReplyEnabled is false on the remote domain
Sender gets the reply only once	By design: one reply per sender per period
Reply still active after return	It was set to Enabled with no end, not Scheduled
Wrong times	Mailbox time zone is wrong, or start and end were entered without a time zone in mind
Reply text garbled	Rich formatting or special characters. Use simple HTML or plain text
Cannot set the reply for a user	Missing role, or the mailbox is on-premises (set it on-premises)
Replies go to a mailing list	A rule replies to everything, or a list setting is allowing it
Shared mailbox reply comes from the wrong name	Display name of the shared mailbox is not set as intended

A Short Decision Guide

• Employee on leave: scheduled reply, Known audience, named contact.
• Customer-facing team address: reply with response times, All.
• Executive or finance: internal reply, None or Known, no travel details.
• Leaver: enabled reply with no end date on the converted mailbox, then review.
• Stop external replies entirely: remote domain setting, but expect side effects.

Related guides: shared mailboxes and leavers, inbox rules, and distribution groups.

Remote domain defaults and cmdlet parameters change over time, and I have not tested these settings in your tenant. Check Microsoft's current documentation and test with a pilot mailbox. If you want help standardizing replies and offboarding, get in touch.