Fix Inbound Email Not Received on IONOS Domain in Microsoft 365
Question details
The user is unable to receive incoming emails sent to a custom IONOS domain after transitioning users from the default onmicrosoft.com addresses in Microsoft 365.
- Product
- Microsoft 365 / IONOS Domain
- Device & OS
- not provided
- Scenario
- Configuring custom IONOS domain email addresses for Microsoft 365 users and managing DNS settings.
- Observed behavior
- Outbound emails are sent successfully, but incoming messages to the custom IONOS domain fail to arrive in the inbox.
Ensure you have administrator access to both your Microsoft 365 admin center and your IONOS domain hosting account to modify DNS records.
Verify Domain Health and Update MX Records
Check the domain status in Microsoft 365 and ensure the correct MX records are set in your IONOS DNS settings to route inbound emails properly.
Inbound email relies on Mail Exchanger (MX) records. If your IONOS domain is missing the Microsoft 365 MX record or has conflicting MX records from a previous email host, incoming messages will not be delivered to your Microsoft 365 inbox.
Sign in to the Microsoft 365 admin center (admin.microsoft.com). Go to Show all, select Settings, and click on Domains. Select your added IONOS domain and check its status to ensure it is healthy.
If health issues are reported, click on Manage DNS to review the affected records. Note the required Exchange Online MX record provided by Microsoft.
Confirm that your custom IONOS domain is set as the default domain for your organization.
Log in to your IONOS account, navigate to the DNS settings for your domain, and add the Microsoft 365 MX record. Delete any old or conflicting MX records that point to other email providers.
Contact Microsoft 365 Support
If your domain status is healthy, MX records are correct, and 48 hours have passed but the issue persists, contact Microsoft Support directly from the admin center.
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Frequently Asked Questions
Why can I send emails but not receive them on my custom IONOS domain?
Outbound emails are sent directly from your Microsoft 365 server and do not strictly rely on MX (Mail Exchanger) records. Inbound emails, however, require external servers to look up your domain's MX records to know where to deliver the message. If the MX record is missing or incorrect, inbound emails will fail.
How do I find the correct Microsoft 365 MX record for my domain?
In the Microsoft 365 admin center, go to Settings, then Domains. Select your custom domain and click on Manage DNS or DNS records. You will find the required Exchange Online MX record, which typically points to a server address ending in 'mail.protection.outlook.com'.
Can conflicting MX records cause email delivery issues?
Yes. If your DNS settings have multiple MX records with the same or similar priority pointing to different email hosts (e.g., keeping an old IONOS MX record alongside the new Microsoft 365 one), email routing will be split or fail entirely. You should only have the Microsoft 365 MX record active.
