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 email@example.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.
Server name: smtp.office365.com
Encryption method: STARTTLS