I have a domain set up with Cloudflare as the DNS provider and I have been using this domain to test Email Routing.
If I set it up as Cloudflare suggests, I seem to receive emails at the designated email aliases with no problem.
However when I attempt to use my mail provider (mailbox-dot-org) to send email, the emails end up showing as Other (failed) in the CF dashboard.
When I add SPF records for mailbox-dot-org, I can send to iCloud accounts and to some other accounts but not Gmail. All of those emails show up as DMARC Failed in the CF dashboard.
Then Email Routing is disabled by CF and it asks me to delete my SPF records and only use their SPF records (without mailbox-dot-org).
Is there any guide out there on how to set this up for sending from a third-party email provider like mailbox-dot-org?