Guides

How to forward Gmail or Outlook to a shared inbox

The confirmation step, the filter path, and the Microsoft 365 policy that blocks external forwarding by default while the setting appears to save — including the bounce code it gives you.

Your Yowl organisation has a working address the day you register, before any DNS change. So the whole experiment below costs one settings page and is undone in a minute.

The cheapest way to find out whether any of this is for you

Forwarding is the only move on this site that touches no DNS, commits to nothing and rolls back in a minute — which makes it the right first step, and it is worth saying what you actually get for it.

Forward one mailbox to your organisation’s address and the team is reading sorted mail within the hour: each message read on arrival, classified, filed under its category, the unrecognised waiting under one Needs a look heading. Nothing has been migrated. Your existing mailbox still has everything. If you hate it, you delete a forwarding rule.

And you can point an AI at it the same afternoon. Connect Claude to the organisation over MCP and “what came in today?” is answerable before you have changed a single record — including “read the attachment on the one from the accountant”, “draft the reply”, and “anything odd about this invoice?”. Drafts wait for a person; nothing sends itself.

That is the whole point of doing it in this order. You find out whether an AI working your mail is worth having before you take on a migration, rather than the other way round. When you decide it is, the rest of the lifecycle is in the same place — point the domain here properly, bring the old mailbox’s contents across, and let the DMARC ladder tighten behind you.

The forwarding itself

This is where the traps are, and one of them wastes an afternoon on Microsoft — skip to that section if a forward you have already set up is not arriving.

Gmail, personal or Workspace

Settings (the gear) → See all settings → Forwarding and POP/IMAP → Add a forwarding address. Enter the shared inbox’s address. Gmail sends a confirmation to it containing both a clickable link and a numeric code, so whoever reads that inbox can either click or paste the code back.

Then pick Forward a copy of incoming mail to and what Gmail does with its own copy — there are four choices, not three: keep it in the inbox, mark it as read, archive it, or delete it. “Mark as read” is usually the one you want when the shared inbox is now the place the mail gets handled.

For a slice rather than everything: Filters and Blocked Addresses → Create a new filter → set the conditions → Forward it to. The address must already be added and confirmed above, or it will not appear in the dropdown.

⚠ If the whole Forwarding section is missing rather than greyed out, a Workspace admin has turned it off: Admin console → Apps → Google Workspace → Gmail → End User Access → Automatic forwarding. Google hides the feature entirely rather than showing a disabled control, which is why this reads as a bug rather than a policy.

Outlook on the web, and “new Outlook”

Settings → Mail → Forwarding → Enable forwarding → the address → tick Keep a copy of forwarded messages. A rule (Mail → Rules → Add new rule → Forward to) does the same for a slice.

⚠ Classic Outlook for Windows has no such setting — forwarding there is done entirely with rules.

⛔ Microsoft 365 blocks external forwarding by default, and lets you save it anyway

This is the one that wastes an afternoon. In Microsoft 365 the outbound anti-spam policy blocks automatic forwarding to addresses outside the organisation by default. The user’s Outlook setting saves successfully with no warning, and then every forwarded message bounces:

550 5.7.520 Access denied, Your organization does not allow external forwarding.
Please contact your administrator for further assistance. AS(7555)

⭐ The default setting is named misleadingly. It reads “Automatic – System-controlled”, which sounds like sensible delegation, and Microsoft currently treats it as forwarding disabled. An admin has to change it deliberately: Microsoft Defender portal → Email & collaboration → Policies & rules → Threat policies → Anti-spam → the outbound policy → Edit protection settings → Automatic forwarding rules → On – Forwarding is enabled. In PowerShell that is Set-HostedOutboundSpamFilterPolicy -Identity Default -AutoForwardingMode On.

Four things worth knowing before you go hunting:

If the bounce persists with no rule visible anywhere, look for a stale mailbox-level forward — the headers will show an ExtFwd action:

Get-Mailbox -Identity 'user@contoso.com' |
  Format-List ForwardingAddress, ForwardingSmtpAddress, DeliverToMailboxAndForward

Also check Mail flow → Remote domains in the EAC, which can block automatic forwarding independently of the spam policy.

What forwarding does to authentication

At the destination, SPF is evaluated against the forwarding server’s IP rather than the original sender’s, so it fails or comes back neutral. DKIM normally survives, because the signature travels with the message — but it breaks whenever the forwarder edits anything signed: prepending [EXTERNAL] to the subject, injecting a disclaimer footer, re-encoding line breaks, altering MIME boundaries or stripping attachments. A plain forward is usually safe; a security gateway in the path often is not. DMARC then passes on the surviving DKIM alone.

For senders who publish only SPF, ARC (RFC 8617) covers the gap: the forwarder records the results it saw on arrival and signs that record. Google and Microsoft both stamp ARC and both trust each other’s chains, which is why a forwarded Gmail message lands cleanly in Outlook without anyone configuring it.

Undo

The forward lives on the source account, so the destination cannot switch it off — only the person who set it up, or their admin. Same settings page.

Connect a domain to Yowl →