 There's a number of different mechanisms that you can use to add things to your SPF record. The most commonly used ones are the ones that I have listed here. So the IPv4 mechanism would allow you to specify a single IP address or one of those CIDR ranges. The A mechanism performs a DNS lookup for the A record for that domain, which is essentially your website. So if you're using your website to send email, like maybe you have a web form and it sends email directly from your web server and not through another service, then the A mechanism is the easiest way to include that. MX would be added if you are sending email from the incoming mail servers for your domain. In your case on Office 365, that would never be the case, so we shouldn't have to worry about that. And the include mechanism allows us to include a DNS lookup for anywhere else on the internet. So for example, those other sources that we were talking about like CRM or mailing services, we would always get an include from those services to add to our SPF record.