What adjustments are required for sending via Mailgun?

In the context of e-mail delivery, the world is constantly changing.
In order to continue to deliver a high delivery percentage, it is possible to have the mail sent via Mailgun.
This is a company, specialized in e-mail transmission, for which the data (can) remain in the EU. This is relevant for the GDPR.

Using Mailgun has consequences for the settings.
There are two options to adjust the mail delivery.

For this you need to know that there are two addresses. 1. The from address and 2. The reply-to address.
The first is the mail from which it is sent. This is checked by the receiver.
The second is the email that is being responded to. So when a recipient clicks on "Reply" from his/her box, the first thing that is checked is whether the Reply to address is known and it is sent to the reply-to address. If not specified, replies will be sent to the from address.

Current situation: you send emails from <mailbox@UWDOMEIN.COM>
And when answers are clicked, the answer also goes there.
Why is this relevant?

There are two options.
1. From = <mailbox@YOURDOMAIN.COM> and Reply-to = <mailbox@YOURDOMAIN.COM>
2. From = <mailbox@YOURDOMAIN.i-reserve.net and Reply-to = <mailbox@YOURDOMAIN.COM>
In both cases a reply will be sent to the <mailbox@YOURDOMAIN.COM> address.
So nothing changes.

In the first case, the administrator of the domain YOURDOMAIN.COM must validate the domain.
This is done with a number of DNS settings. These can be requested from our support, will be sent to you and must be configured by the DNS administrator.
So access to DNS is needed.
In the second case, the shipment can be arranged entirely within i-Reserve support and the DNS administrator of the domain does not have to do anything.

In both cases, the mail transmission is provided with both SPF and DKIM.