Hi @Evgeny Melnikov,
Welcome to Microsoft Q&A Platform. Thank you for reaching out & hope you are doing well.
I am afraid to say that it is not possible unless you are the admin of the domain.
"Microsoft.com" is a corporate domain owned and managed by Microsoft, and typically, individual employees do not have the ability to add or configure custom domains under such a corporate domain without going through official channels.
Since "microsoft.com" is a corporate domain, you will need to seek approval from your internal IT or domain management team. You cannot directly set up "microsoft.com" as a custom domain for your Azure Functions App without going through the appropriate internal channels. They will have the authority to configure email settings and manage domains.
Please contact your Admin for assistance in setting up the necessary configurations and permissions.
Kindly let us know if the above helps or you need further assistance on this issue.
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Regards,
Sai Prasanna.