If you have an existing address on your own domain, migrating to Port87 is easy.
First, you'll need to sign up for Port87's Domain Owner subscription. You can do that on your subscription page.
Next, you'll need to onboard the domain name to Port87. We have a video tutorial that walks you through purchasing and onboarding a domain name:
Since you already have your own domain, you can skip through the domain purchase portion. When it comes to adding the DNS entries, you can leave any existing DKIM records, but the DMARC, SPF, and MX records should be replaced with the ones for Port87.
Once you have onboarded your domain, you can recreate your username from your old provider, then you will start receiving mail through Port87. If you have configured your domain as a personal domain, this is as simple as creating a label with the ID of your old address' user portion. If you have configured your domain as a multi-user domain, you can choose your old address as your username when you onboard your domain.
For multi-user domains, your address will act like a regular Port87 address by default, auto-responding to mail addressed to your "bare address" (yourname@example.com) with a list of the public label addresses for the domain. If you'd like to receive this mail to a label instead, you can check the "Accept email to your bare address" checkbox in the label edit screen for the label you want to get this email.

Though you can leave this option enabled forever, we recommend migrating all of your accounts and contacts to have their own labels, then disabling this option. This helps with organization, and is the recommended way to get the most from Port87.
If you need to create additional addresses for other users, you can change the "Quantity" of your subscription to enable more users. Then you can create accounts for them in the "Users" section under "Domain Management" in your Port87 settings. If they need to receive mail to their bare address, they can enable the "Accept email to your bare address" checkbox on one of their labels.