A cloud-based service included in Microsoft 365, delivering scalable messaging and collaboration features with simplified management and automatic updates.
To ensure I fully understand your situation and provide the most effective assistance, I’ll need a few additional details, such as:
May I know whether the affected account is hosted and managed via Exchange Online, on-premises Exchange, or another email provider?
Does this behavior affect all messages sent to Gmail recipients, or only some recipients?
Do you receive any NDR (bounce-back message) or a specific error code when the email is rejected?
Additionally, you could also refer to this article for guidance on configuring DKIM for your account: How to use DKIM for email in your custom domain - Microsoft Learn
Any update would be appreciated.