Microsoft Outlook Accounts can be configured as the default sending account or for individual users.

Account Limits Imposed by Microsoft:

• 30 emails per minute per configured email — If your app sends individual emails, this is your main short-term rate limit.
• 10,000 recipients per 24 hours per configured email — Each person you send to counts as one recipient. This is a rolling 24-hour limit.
• For High Volume, this limit on your main sending account is likely to be hit which will result in emails failing to send. For the main sending account we recommend to configure the Microsoft email through Sendgrid. use standard smtp, not microsoft sender type.

From Settings / Integrations / Email - Select Microsoft:

Where Do I Get That Information From Microsoft?

On Each Outlook Account you would like to connect, you will need to pull the Azure Client Information as follows:

You will need:

• Email → the actual Microsoft 365 mailbox you want Airstudio to send from, e.g. [email protected] — not apikey.
• Azure Client ID → Microsoft calls this Application (client) ID.
• Azure Client Secret → a secret you create for the app. You need to copy the Value, not the Secret ID.
• Azure Tenant ID → Microsoft calls this Directory (tenant) ID. (Microsoft Learn)

Here's how to create them:

Go to the Microsoft Entra admin center and sign in with an administrator account for the Microsoft 365 organization that owns the Outlook mailbox.

Go to Entra ID → App registrations → New registration.

I'd name it something like Airstudio Email.

If this is just for connecting your organization's Microsoft 365 account to your Airstudio instance, choose Accounts in this organizational directory only (Single tenant) and click Register. Microsoft specifically describes single-tenant apps as apps intended for users within one tenant. (Microsoft Learn)