To authorize Apptoto to send emails on your behalf you will have to manually add it to your SPF record. The SPF record mechanism used for Apptoto is as follows:
Apptoto also support DKIM signing, in order to enable it please contact their support team here: [email protected] and request DKIM to be enabled for you custom domain.
Check if DKIM is configured correctly
Why not use our free Investigate tool to swiftly verify your DKIM configuration.
Create a free OnDMARC account to test your configuration.