EmailOctopus uses Amazon SES as their email platform, therefore to authorize EmailOctopus to send emails on your behalf you will have to include Amazon SES in your SPF record. The SPF record mechanism used by Amazon SES is shown below.
However, to pass DMARC validation based on SPF you will need to configure a custom Mail From domain as per the instructions below.
EmailOctopus / Amazon SES does support DKIM signing. Please follow the EmailOctopus instructions using the button below.