These instructions will walk you through how to add an SMTP server to an existing Outlook 2016 setup, but you can also add these settings at the account creation stage.
Navigate to the setting of Outlook desktop application on Mac:
On next screen, please select IMAP/POP. Bonus tip: Outlook on Mac does not give you this next option directly. In that case, please try an email as abc@example.com and you will get the next pop-up window.
Set Outgoing server details as:
Outgoing server: smtp.sendgrid.net
SendGrid accepts unencrypted and TLS connections on ports 25, 587, & 2525. You can also connect via SSL on port 465. Many hosting providers and ISPs block port 25 as a default practice.
Here in this example I am going to use default port as 25 and uncheck the SSL option.
Please note Incoming Mail Server: This can be your usual IMAP server (not SendGrid).
Next, click More Options and enter the information as shown below.
Set Authentication as Username and Password
Username: apikey
Password: Here you need to pass the original API key you can generate from your SendGrid account: https://app.sendgrid.com/settings/api_keys
Finally, click on OK, and you should be all set at this point. If you need more assistance, please contact support.
Please note that the exact steps might slightly vary depending on the version of Outlook. Additionally, make sure to input the correct SMTP server, port, and authentication details provided in this SendGrid help article.