And want to add tha DMARC and DKIM (email sending domains) are not currently supported in HubSpot Marketing Free accounts. If your organization has a DMARC policy in place, you’ll want to make sure SPF and DKIM are set to ‘relaxed’ alignment.
However, HubSpot’s suggestion to include an SPF entry in our DNS records is ineffective and plain bad advice, unless subscribed to their “Dedicated IP” service ($$$$$). You see, otherwise, the return-path entry in each HubSpot email will authenticate using their DNS records/servers, not ours.