Custom email domain on Outlook

I have just bought a domain for my wordpress website on hostinger for my client. In the package she got an email with a custom domain. My client wants to send and receive all the mails coming from the custom email in her outlook, with all her other emails.

I have been searching everywhere and can’t find an answer. Somewhere I saw that outlook stops allowing custom emails, I don’t know if it’s true or not.

I found it a lot easier to connect the custom email on gmail than outlook.