Can I use an e-mail alias to collect e-mail from a legacy domain address

Hi,

   I manage (very part time) an Office 365 instance for an NGO. When we set up the Office 365 back in 2016, we changed to a new domain name and migrated all mailbox content from their previous domain provider. However, the important task of decommissioning the legacy domain was never completed. Three years later and I find that some users still monitor their old e-mail addresses for mail.

I need to shut down the legacy e-mail service. Apart from the messiness, it is a paid service.

I'm sure this is not a new question but a search did not turn up a specific answer, so is this the right approach:

1. Add the legacy domain to the Office 365 instance
2. Allow Office 365 to manage the DNS, which will point the MX records to Office 365
3. Add e-mail aliases for the old domain addresses to all users still receiving e-mail on the old domain.

Thank you.