Integrations · Outlook and Slack

Outlook to Slack automation that your admin won't bounce

When an important email reaches your Outlook mailbox, post it to the right Slack channel with a short summary. No forwarding rule, so no 5.7.520 bounce.

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The ClearMakes Inbox team · Last updated 29 September 2026

What is the Outlook to Slack workflow in ClearMakes Inbox?

It is a ClearMakes Inbox workflow that watches an Outlook mailbox and, when a new email matches what you described, posts it to a Slack channel. It reads the mailbox through a connected app, not a forwarding rule. You set it up in one sentence; there is a free plan, and paid plans start at $29 a month.

What the Outlook to Slack workflow does

It picks the Outlook emails that matter and posts them where your team already talks. Everything else stays in Outlook.

Example workflow

“When a new Outlook email comes from a client domain, post the sender, subject and a two-line summary to #clients.”

When an email arrives in Outlook
Check it is from a client
Summarise it
Post to #clients in Slack

Example workflow

“When someone sounds upset in an email, message the account owner in Slack straight away.”

When an email arrives in Outlook
Stop if the tone is calm
Post a direct message in Slack

How to set up Outlook to Slack

Connect Outlook and Slack, describe the workflow in a sentence, check the steps, and switch it on. You need an Outlook or Microsoft 365 mailbox and a Slack workspace where you can add apps.

Create a free ClearMakes account
Start from ClearMakes Inbox.
Connect Outlook
Open Apps, find Outlook and choose Connect. Microsoft's sign-in screen shows the permissions. A work account may need your admin to approve the app.
Connect Slack
Do the same for Slack and pick the workspace.
Describe the workflow
In Workflows, type what should happen, for example the client example above.
Check the steps and switch it on
Inbox writes the steps and asks at most one question. Change anything you like, create the workflow and switch it on.
Check the first runs
Each run is listed with its steps and the exact post that went to Slack.

Other ways to get Outlook email into Slack

A forwarding rule to Slack's channel email address is free if two things are true: you pay for Slack, and your Microsoft 365 admin allows forwarding to outside addresses. Otherwise you need a connected app.

Ways to send Outlook emails to Slack
Way	What it costs	Good at	Watch out for
Outlook rule forwarding to Slack's channel email address	Included in paid Slack plans	Copying every matching email into a channel	Slack's email address is paid plans only; many Microsoft 365 organisations block automatic external forwarding (bounce 5.7.520)
Zapier (Outlook + Slack)	Free: 100 tasks a month, checks every 15 min. Professional: $29.99 a month for 750 tasks	Many Outlook triggers and Slack actions	Each successful action is a task; reviewers report Outlook triggers that stop firing
IFTTT	Pro: $2.99 a month	Very cheap for one simple rule	Outlook trigger is polled: every hour on Free, every 5 min on Pro
ClearMakes Inbox	Free: 3 apps, 100 runs a month. Starter: $29 a month for 5,000 runs	Choosing which emails matter, summaries, delays and wait-for-reply in one workflow	Newer and smaller than Zapier; fewer ready-made templates

Checked on 29 September 2026: Microsoft, control external email forwarding, Slack, Send emails to Slack, Zapier pricing, IFTTT plans, and a Zapier community thread, “new emails in Microsoft Outlook aren't triggering my Zap”.

Limits, and who this is not for

If your team lives in Microsoft Teams rather than Slack, use Outlook to Teams instead. If you need every email copied word for word and your admin allows forwarding, a rule is simpler.

Teams users: see Outlook to Teams.
Not a shared inbox: replies still go from Outlook.
AI checks and summaries can be wrong now and then. Look at the first runs before you rely on them.
Shared mailboxes: connect the account that can open the shared mailbox. Whether a given shared mailbox can be watched depends on its Microsoft 365 set-up.

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Questions people ask

Why does my Outlook rule to Slack's email address bounce?

Many Microsoft 365 organisations block automatic forwarding to outside addresses. Since 2021 it is off by default for new organisations, and the sender gets a 5.7.520 “Access denied” bounce. Ask your admin, or use a workflow that posts to Slack instead of forwarding.

Does it work with a Microsoft 365 work account?

Yes, if your organisation lets you connect outside apps. Some admins must approve a new app first; if Microsoft asks for admin approval when you connect Outlook, send the request to your IT admin.

Can it post a summary instead of the whole email?

Yes. Most people post the sender, the subject and a two-line summary. Say what you want in the sentence, for example “post a two-line summary”, and check the step before you switch it on.

Is there a free way to try it?

Yes. The free plan covers 3 connected apps, 2 new workflows a month and 100 runs a month. Outlook and Slack use two of the three apps. Starter is $29 a month for 5,000 runs.

Can I reply to the email from Slack?

Not from inside Slack. The workflow posts to Slack; replies still go from Outlook. A workflow can draft a reply in Outlook for you to check, if you ask for that step.

Keep reading

Post the Outlook emails that matter to Slack.

Connect Outlook and Slack, type one sentence, and check the steps.

Try Inbox free

Free plan: 3 apps, 2 new workflows and 100 runs a month.