Send & Receive Issues

Fix Business Central OutboundSpamException and RefuseQuota Errors in Outlook

Maira Mehtab Sep 21, 2026 869 views

Question details

The user needs to resolve an outbound spam exception and quota refusal error when attempting to send emails through Microsoft Dynamics 365 Business Central using an Outlook account.

Product: Microsoft Dynamics 365 Business Central / Outlook
Device & OS: not provided
Scenario: Sending outbound emails from Business Central using Basic authentication with an Outlook email account.
Observed behavior: Email sending works briefly and then fails, displaying a 5.2.0 STOREDRV.Submission.Exception: OutboundSpamException error with a RefuseQuota and ShowTierUpgrade verdict. Previously failed messages return to the Outbox.

Before you start

Verify your current network connection and ensure you have your Outlook webmail credentials readily available before troubleshooting your mailbox status.

Solution 1Recommended

Verify Account Type and Test Webmail Access

Determine if the issue is tied to specific account limitations by testing email delivery directly through Outlook on the web.

Personal Outlook.com accounts and Microsoft 365 business accounts have different supported authentication methods and sending limits. Isolating the issue to the webmail interface helps confirm if the problem lies with the mailbox itself rather than the Business Central setup.

Identify your account type

Review your email settings in Business Central to confirm whether you are using a personal Outlook.com address or a Microsoft 365 business account.

Log into Outlook on the web

Open a web browser and navigate to outlook.live.com (for personal accounts) or outlook.office.com (for business accounts), then sign in.

Send a test email

Compose a new email from the web interface and send it to another address you own to see if it delivers successfully.

Analyze the webmail results

If sending from the web also fails or throws a quota error, the issue is related to your mailbox's outbound spam controls or account restrictions, not Business Central.

Authentication Warning: Basic authentication is being deprecated by Microsoft. Switching to Modern Authentication (OAuth) in Business Central may resolve underlying connectivity drops.

Solution 2

Review Sending Limits and Resolve Quota Restrictions

Check your Microsoft account for outbound quotas or service-tier restrictions that trigger the RefuseQuota verdict.

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Frequently Asked Questions

What does OutboundSpamException mean in Business Central?

This exception occurs when the Microsoft Exchange server flags your outgoing emails as potential spam. In automated systems like Business Central, this often happens if you send too many emails in a short period, triggering Microsoft's automated outbound spam filters.

Why am I getting a RefuseQuota verdict when sending emails?

The RefuseQuota error indicates that your email account has reached its daily or hourly sending limit. This is especially common with free, personal Outlook.com accounts which have strict limits to prevent spam.

Can using Basic authentication cause email delivery issues in Outlook?

Yes, Microsoft is actively deprecating Basic authentication across its services. Continuing to use Basic authentication can lead to connectivity drops, security blocks, and email failures. It is highly recommended to configure Business Central to use Modern Authentication (OAuth 2.0).

How can I fix the ShowTierUpgrade error in my email logs?

The ShowTierUpgrade verdict typically means your current account subscription tier does not support the volume of emails you are attempting to send. To fix this, you generally need to upgrade from a free account to a paid Microsoft 365 business plan to increase your outbound limits.

Outlook & Email Problems