For your provider

Amazon SES

Amazon SES uses a subdomain of amazonses.com as the default MAIL FROM. A custom MAIL FROM needs the SPF v=spf1 include:amazonses.com ~all and exactly one MX record.

v=spf1 include:amazonses.com ~all

The MX Amazon SES publishes is 10 feedback-smtp.{region}.amazonses.com. The MAIL FROM domain has to be a subdomain of a verified identity, and Amazon SES says it must not also be used to send or receive mail. More than one MX on that name fails the custom MAIL FROM setup. The {region} is the AWS Region, for example us-east-1. SPF alignment for DMARC still needs the From domain to match that MAIL FROM domain.