Your Business Central Email Will Break Soon: How to Future-Proof Your Setup Today

Microsoft is retiring SMTP Basic Authentication.
If Business Central shows the warning that SMTP is still in use, the root cause is simple:

👉 One or more Email Accounts in BC are still defined as SMTP Accounts.

Here is the clean, correct, and complete path to resolve the warning, modernize your email setup, and fix the “blocked” error during testing.

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Step 1: Identify which Email Accounts in BC are still SMTP

In Business Central:

1. Search Email Accounts
2. Open each account
3. Look at the page caption at the top

You will see one of two types:

✔ “Microsoft 365 Account”

Already correct.
Uses OAuth through Microsoft Graph.
No action needed.

❌ “SMTP Account”

This is the one causing the retirement warning.
SMTP accounts cannot be converted — they must be replaced.

There is no “inactive” option for email accounts, so these will be deleted after you create the new Microsoft 365 version.

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What happens if you have both SMTP and Microsoft 365 accounts for the same mailbox?

Business Central decides which account to use based on Email Scenario assignments, not the email address itself.

And each scenario can be assigned to only one email account at a time.

This means:

• If any scenario is still assigned to the old SMTP Account, BC will continue trying to send through SMTP
• The SMTP retirement warning stays active
• You may still get SMTP 535 authentication failures, even though the Microsoft 365 account is present
• BC will never automatically switch to the M365 account unless you reassign the scenario

Fix:
After creating the new Microsoft 365 account, assign it to the scenarios and then delete the SMTP account.

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Step 2: Confirm the prerequisites before adding the new account

If your shared mailbox has been working up to now in BC, this is already true — but it must be stated:

✔ The person creating the account in BC must already be able to Send As that shared mailbox
✔ Sending as the mailbox must already work in Outlook Web or Outlook Desktop

Quick test:

1. In Outlook, create a new email
2. Change From to the shared mailbox
3. Send a message to yourself
4. If it arrives from the shared mailbox, permissions are correct

If Outlook cannot send as the shared mailbox, BC will not be able to either.

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Step 3: Create a new Microsoft 365 Email Account in BC

In Email Accounts:

1. Select New
2. Choose Microsoft 365 as the account type
3. Enter the shared mailbox email address
4. Save
5. Select Send Test Email

Important:
There is no Authenticate button.
The Microsoft 365 account type uses OAuth automatically during the test.

If you see SMTP server fields like smtp.office365.com, you selected the wrong account type.

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Step 4: Expected error — and why it happens

Your first Test Email usually fails with:

“The request to send email has been blocked. To resolve the problem, enable outgoing HTTP requests for the Email – Outlook REST API app on the Extension Management page.”

This is expected.
BC is now using Graph-based sending but the extension that calls Microsoft 365 is still blocked from making outbound HTTP requests.

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Step 5: Enable outgoing HTTP requests for the Outlook REST API extension

1. Search Extension Management
2. Open the extension:
   Email – Outlook REST API (Publisher: Microsoft)
3. Choose Configure
4. Turn Allow HttpClient Requests → On
5. Save
6. Return to Email Accounts and send Test Email again

This time, it will succeed.

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Step 6: Assign the new Microsoft 365 account to Email Scenarios

1. Search Email Scenarios
2. Assign the new Microsoft 365 account to each scenario that previously used SMTP
3. Save your changes

This ensures BC always uses the modern account.

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Step 7: Delete the old SMTP Account

1. Go back to Email Accounts
2. Open the old SMTP Account
3. Choose Delete

Once the SMTP account is removed:

• The Microsoft retirement warning disappears
• BC stops attempting SMTP for any scenario
• Email sending becomes more reliable and future safe

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Why this works

✔ Removes all SMTP dependencies
✔ Switches BC to Microsoft Graph OAuth
✔ Eliminates authentication failures
✔ Meets Microsoft’s requirements for March 2026
✔ Ensures BC email continues working long term

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Sharing the Righter Way^TM

Created as part of Sharing the Righter Way, this article combines my Business Central experience with AI supported research and drafting. AI helps me explore options and accelerate analysis, while every conclusion and recommendation reflects my own professional judgment.