Zendesk is capable of sending DMARC compliant email because they support custom SPF and DKIM configurations that achieve alignment. This source is most commonly known to send customer support emails and is often used by Customer Service and IT help desk teams.
The link just below is a resource on how to configure DKIM. You will complete this configuration by (1) following the sources instructions and (2) adding the required entries into your DNS. https://support.zendesk.com/hc/en-us/articles/4408822303386-Digitally-signing-your-email-with-DKIM *Note: As part of the custom DKIM configuration, you will be prompted to create two CNAME entries. These allow the source to rotate DKIM keys automatically.
The link just below is a resource on how to configure SPF. You will complete this configuration by (1) following the sources instructions and (2) adding the required entries into your DNS. https://support.zendesk.com/hc/en-us/articles/4408832543770 *Note: Both SPF and domain verification steps are required.