SMTP
(Simple Mail Transfer Protocol) is used when you set up an on-premises multi-function printer, scanner, fax, or line of business (LOB) application that needs to send email. If some or all of your mailboxes are in Office 365, there are a few options available: SMTP relay, client SMTP submission, or Direct Send
SMTP Relay
An SMTP relay is used to send mail from your organization by authenticating the IP address or certificate of the sender. Any email address (including non-Office365 mailboxes) can send mail using an SMTP relay, as long as it uses a domain that’s set up as yours in Office 365.
Client SMTP Submission
Client SMTP submission allows your device or LOB application to send emails using an email address associated with an Office 365 mailbox by authenticating itself using that account. Each device can have their own sender address or all devices can use one address such as printer@yourdomain.com.
Direct Send Direct Send can be used if the device or LOB application has the ability to send mail by itself. If so, the device or LOB application does not use Office 365 to send the mail, but the mail is received by Office 365 for delivery to your Office 365 accounts.
| Option | SMTP Relay | Client SMTP Submission | Direct Send | ||
|---|---|---|---|---|---|
| Send to recipients in our domain(s) | Yes | Yes | Yes | ||
| Relay to Internet via Office 365 | Yes | Yes | No. Direct delivery only. | ||
| Configuration requirements |
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| Requires authentication | No. IP address provides authentication. | Yes. However if the device does not support this option, you can use on-premises Windows SMTP relay. | No | ||
| Bypasses anti-spam | No. Suspicious emails may be filtered. We recommend a custom SPF record. | Yes if the mail is destined for an Office 365 mailbox. | No. Suspicious emails may be filtered. We recommend a custom SPF record. | ||
| Throttling Limits | Reasonable limitsare imposed. The service cannot be used to send spam. | 10,000 recipients per day. | None | ||
| Licensing requirements | Requires Exchange Online Protection licenses for each sender. Office 365 mailboxes have this license. | Can use a standard or shared mailbox. | Email sender licensing not required. | ||
| FQDN of SMTP Endpoint | To obtain the string for your domain, go to Domains in the Office 365 Portal. | smtp.office365.com | No endpoint required. This method uses DNS based routing. |
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