Email Source: Doppler

Homepage: https://www.fromdoppler.com

This source is known to forward email

Capable of generating DMARC compliant email for others

Yes

Doppler supports DMARC compliance via DKIM.

Capable of signing email with DKIM for others

Yes

Contact Doppler support for DKIM setup.

Capable of sending SPF compliant email for others

No

Doppler doesn't seem to support compliance via SPF at the moment. Contact their support for more information.