Options to Send Emails using Microsoft 365

This is how to send emails from an app or device not named Outlook through the Microsoft 365 network. According to Mail Flow Best Practices, there are 3 options available.

  • SMTP Auth
  • Direct Send
  • SMTP relay


If you can deal with Modern Authentication in the form of OAuth, this option provides you with the most reliable email delivery. And you do need a licensed mailbox to send emails from.

Server/smart hostsmtp.office365.com
PortPort 587 (recommended) or port 25
Username/email address and passwordEnter the sign-in credentials of the hosted mailbox being used

Direct Send

Direct Send doesn’t require SMTP Auth, nor a licensed mailbox. All you need is to specify your own MX endpoint as the mail server or smart host with an unblocked Port 25, you are all set to send emails to recipients in your own organization. Adding an SPF record to avoid having the message flagged as spam is recommended but not required.

v=spf1 ip4: include:spf.protection.outlook.com ~all
Server/smart hostYour MX endpoint, for example, contoso-com.mail.protection.outlook.com
PortPort 25
Email addressAny email address for one of your Microsoft 365 or Office 365 accepted domains. This email address doesn’t need to have a mailbox.

SMTP Relay

If you need to send emails to external recipients, or not every device on your network has Port 25 open or allowed, SMTP Replay could be your answer. The basic setup is the same as the Direct Send but you do need to set up a Mail Flow connector first, whether it’s certificate-based or IP-based.

Obviously, an IP-based connector is much easier.

Connector settingValue
FromYour organization’s email server
ToMicrosoft 365 or Office 365
Domain restrictions: IP address/rangeYour on-premises IP address or address range that the device or application will use to connect to Microsoft 365 or Office 365
Device or application settingValue
Server/smart hostYour MX endpoint, for example, yourdomain– com.mail.protection.outlook.com
PortPort 25
Email addressAny email address in one of your Microsoft 365- or Office 365-verified domains. This email address doesn’t need a mailbox.

And again, SPF is highly recommended to avoid your messages being trapped in the spam folder.

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