Receive email form sub-domains without creating the sub-domain

Hello,
We use Exchange online for our company email. We have external company’s and services
how sending mail on behalf of us. For this we use an email subdomain, for example: helpdesk.comtoso.com. this works fine
The problem is receiving email. If we want to receive email, we must create the email domain,
This also creates a login domain. There are about 10 email sub-domains, and this number is growing.
We are looking for a solution to receive mail, without creating the sub-domains in Exchange online.

Are there cloud services that receive and forward mail directly? Our other solutions.

Any help is much appreciated

Kind regards Finn