In order to authorize ProtonMail to send emails on behalf of your custom domain you will have to add them to your SPF record. The SPF entry used by ProtonMail is shown below.

include:_spf.protonmail.ch

Configuring DKIM signing is different for each email provider. For instructions on how to configure DKIM with ProtonMail please click on the button below.

Create a free OnDMARC account to test your configuration.