Outlook Silently Dropping Transactional Emails from Our Domain

Question

Hello Microsoft Community,

We are experiencing an issue where emails sent from our notifications address are silently dropped by Outlook / Office 365 recipients without reaching the inbox or junk folder. The details are:

• Sending Service: Resend
• Recipients: Outlook.com, Office 365 business users
• Behaviour: Emails do not appear in inbox, junk, or spam folders, and no bounce is received.
• Other Providers: Gmail, Apple Mail, Yahoo, etc. receive these emails without issues.
• Authentication: SPF, DKIM, and DMARC are properly configured and passing alignment checks.

Could anyone advise:

1. Why Outlook might silently drop these emails without placing them in junk or notifying the sender?
2. Whether there is an additional process for getting our domain/IP approved or whitelisted by Microsoft for transactional notifications?

This issue is impacting user onboarding, and any insights or escalation guidance would be greatly appreciated.

Thank you in advance for your support.

Best regards,
Yun-Chi

Answer 1

Hello,

Do make sure your SPF, DKIM and DMARC are configured correctly because Microsoft is strictly enforcing it now since May.

Otherwise, reach out to the Delist portal https://sender.office.com/ See if your IP might be on the blocked list.