Office365 subdomains

[Mabahma]

Hello

I ve a test O356 tenant with a principal domain test.dom.com

I m creating two groups of users:

One with e-mails in the form of : xxxx@test.dom.com

and another with emails in the form of:

xxxx@sub.test.dom.com

Should i use another tenant to manage the two groups?

If i can do this in one tenant..how can this be realized?

Thnx

[#2]

You just need to verify domain test.dom.com in O365, once you do you can add multiple subdomains.
So if you have already verified test.dom.com in O365 you can add sub.test.dom.com from 'Domains' option under 'Settings' in Admin Portal and no additional verification or TXT record is required to prove ownership of this subdomain.
However you still need to add MX and other records for mailflow and autodiscover to work correctly for this subdomain.

[#3]

Thank you

Is Azure Ad going to manage the two domains correctly?

Do u have an example on how to set mailflow for this case
Br

[#4]

Once you add and verify test.dom.com, you can add sub.test.dom.com. During the domain add process you will be provided with DNS records that you need for mailflow, you just need to add those to your public DNS.
Azure AD can manage your domains correctly as long as you set them up correctly and add the required DNS records correctly.