Office 365 - Multiple Tenants under One Account

First, I believe an account with Microsoft refers to one tenant. There is no reference of one account with many tenants.

Unless you operate this as a service provider business,  then you may possibly have one service provider account with multiple customer tenants. This will require you to register as a Microsoft CSP (Cloud Service Provider) with a CSP distributor.

Within one tenant you can have many domains, but this assumes that these domains are all under the purview of a single organization (eg a company with many subsidiaries).

Each domain has its own dns, and settings within. 

To improve email delivery scores, consider turning on DKIM for each of the domains, and setting DMARC (quarantine or reject) as well. Do so only after careful study else any form of legitimate email impersonation will be affected.

Hello YG2020,

Based on my knowledge, if you have a Microsoft 365 subscription, it is not feasible to create different onmicrosoft tenants for different domains with the same subscription. Besides, the DNSs of the domains are actually separate and indeed operated separately. Also, these domains have their own DNS records and won't affect each other. So please make sure you verify each domain in the same tenant successfully and their status is healthy to prevent the unexpected issue. For your reference: Add a domain to Microsoft 365.

If I misunderstand your meaning or you need more help, please feel free to let me know.

Regards,

Seven

I have done exactly the same. I do think though the domains in mail servers eyes all look at them the same on that tenant. In the DKIM settings you have to put an omnimicrosoft account. ALl of them share that same base tenant email omnimicrosft account unless you have figured out a way to put in a different email address for DKIM. I think that is the loop that makes all their health and deliverability be coupled together.

I have a number of domains on my own Office365 tenant.

Each domain requires a seperate SPF, DKIM and DMARC records in their respective DNS servers.

For example if I own contoso.asia and acme.asia, I have to set SPF, DKIM and DMARC for each of these domains in their own dns page. I also have to turn on DKIM within office365 specifically for each domain.

To set DKIM, go to Admin -> Security->threat management->Policy->DKIM

You will see the domains you have in your office365 tenant.

When you try to turn on DKIM for a particular domain (and if you have not added the appropriate CNAMEs into the domain's dns), the system will prompt you with an error message giving you the correct entries you need to make into the DNS for that domain.

I have set these up and they are working properly for my domains.

Do note that Office365 uses a CNAME to create the DKIM function in DNS rather than the usual TXT field used by other email providers like google.

Thank you so much. The part that raises concern for me is in order to activate the DKIM, it connects to the tenante omnimicrosoft account. Thus, all domains within the account activated with DKIM share that same omnimicrosoft. I have noticed that as I use the domain more and try a new domain with those settings, I run into an issue with emails going directly to spam/categories. I have a service that monitors this info and seeing as I start new domains that happens. Any idea how to separate the DKIM out or DNS? Thats why I was going for multiple tenants because I sense the reputation is all coupled together.