The Kinvey platform uses the Sendgrid eMail Service for all its email delivery. This includes the "email" module in Business Logic and Flex, as well as emails that are sent as part of the user subsystems: email verification, forgotten passwords, etc.
In each of these systems, a Kinvey developer can set their own "From" address. This has implications in modern-day email acceptance, where "From" addresses are checked against a positive confirmation from the parent domain. SPF (Sender Policy Framework) allows a domain to specify which mail servers are allowed to send email on its behalf, which will prevent any other mail server from sending spam or fake emails.
If you are using Kinvey to send email on behalf of your own domain, and your domain implements SPF, then you must add Kinvey's eMail delivery service (Sendgrid) as an allowed sender to your DNS. For instance, if you are a developer for "Acme Health" and you are using Flex or BL to send email from "firstname.lastname@example.org", then you must add rules to your acmehealth.com DNS to allow Sendgrid to send these emails on acmehealth's behalf.
Adding SPF records to your company's own DNS is sometimes called "email whitelisting".
Instructions on how to add Sendgrid to the SPF records in your company's DNS can be found at the following link.