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To maximize deliverability (i.e. the percentage of messages delivered to the Inbox, not the Spam folder), we need to let email receivers know that these two entities are related. That it is OK for us to send your email and that it is OK for your provider to send your email with us.
Otherwise, email receivers may penalize your messages. The way they do that is to either outright reject your emails, or - more commonly - place them into the spam folder.
So, we need to tell them that it is OK for them to receive an email from "us" (our system) with "you" (your domain name) as the "fromFROM" address.
That is where email authentication comes in: SPF, DKIM and DMARC are the industry standard practices for properly authenticating your emails.
This can be done in two ways.
You tell them
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This is the recommended approach.
In this approach, you tell email receivers that it is OK for us to send your emails by adding some information to your domain registration details.
It's what we refer to as "email authentication". SPF, DKIM and DMARC are ways to authenticate an email.
You will authenticate your emails using your domain.
We tell them
We tell them that it is OK. This is done by using something called "sender header". We basically add some information to your email clarifying to email receivers that the "from" is actually "us", sending on behalf of "you".
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If you don't want this message to show, use email authentication.authenticate using your own domain