Below is a list of the most common SPF include mechanisms used by third party email service providers.
Microsoft Office 365
Single include SPF record example:
v=spf1 include:amazonses.com ~all
The above SPF record indicates that only Amazon is authorized to send emails on behalf of your domain.
Multiple includes SPF record example:
v=spf1 include:mailgun.org include:_spf.google.com include:spf.protection.outlook.com ~all
The above SPF record indicates that Mailgun, Google and Microsoft are authorized to send emails on behalf of your domain.