What is the max number of domains Office 365 supports? Microsoft confirms: there is no limit

If you have a need to load in a large number of domains into Office 365, you could be searching the internet frantically to find out the answer to the question posed in the title of this post. That’s exactly what I did when doing some timely research for a new customer looking to take their entire corporation under the flag of Office 365. Hours of searching with no official answer as to how many domains the Office 365 platform can natively support.

I started off my hunt scouring the official Office 365 support forums and happened to stumble on this thread which was from 2011. The post highlights a user which was attempting to get about 1000 domains verified and added into Office 365. That’s quite a large number of domains! Regardless of the reason for needing to do so, Microsoft should make this answer easier to find. This post did little to allay my curiosity – and basically admitted that there was no documentation available providing an answer in one direction or another.

Similarly, this post also surfaces quite easily at the top of the list after doing some searching, and it is also just as scarce in terms of quality answers. A Microsoft MVP jumped into the conversation to state that he believed the answer was “in the hundreds” but there was no solid proof that this was true. The post left me searching even further for the truth now, seeing that multiple posts had yet to answer the question.

I took my hand at the issue and decided to post a question to the Office 365 forums and actually got a response from Microsoft support. Surprisingly, this time we were getting somewhere. The agent posted a link to this page on the Office 365 support area which states in the footnotes that there is a 600 domain limit in Office 365. However, the suspicious part about this page is that it has no revision date like the rest of the Office 365 support pages – which means, in all honesty, this information could be outdated by months if not years by now! The page itself follows the same formatting and styling as the 2013-release based Office 365 support pages, but still, this does not ensure comfort for a client of mine that is about to make a multi-thousand dollar decision on moving to Office 365.

Below is a screenshot from this webpage on their support site:

The customer we are working with has a peculiar situation, perhaps not that uncommon among large franchiser-styled organizations where individual branch locations were allowed to open their own email systems tied to domains which were purchased without corporate oversight. So over a decade or more, this adds up to hundreds of branches that are operating their own email domains under various flags. I am not going to name the customer by name, but I will say that they are a national leader in the retail automotive parts industry. This clean up effort on the behalf of the corporate office is an attempt to bring everyone under the same system so that all branches are allowed to have namesake corporate email accounts, and for easy collaboration across all locations. Legal retention, 25GB email inboxes, and integrated Lync Online are all important pieces of the puzzle for them.

Not feeling comfortable with the information from Microsoft’s online forum support rep, I decided to reach out to the Microsoft Partner Network USA hotline. Since our company is an Office 365 cloud services partner, we are entitled to some pretty good support on issues like this. So after calling in, I was told that an answer was not readily known off the bat, but that I would get an email with a solid definitive answer.

Surely enough, after waiting two days, I got what I was looking for. A Microsoft rep by the name of Mary got me an answer straight from the horse’s mouth, or more accurately a tech consultant that works either on or with the Office 365 for Business team (I presume). Below is a carbon copy of what I was emailed as a response:

Hello Derrick,

Thank you for contacting the Microsoft Partner Network.

As I promised I verified the information related to maximum amount of Domains you can have under a tenant/.onmicrosoft.com and the answer is: There is no limit.

I got this information directly from the Technical Consultant.

If you have further questions please do not hesitate to contact us. Our contact information is listed below.

Thank you for contacting Microsoft.


This was pretty great news. I am going to trust the statement of the Microsoft Partner rep because I know for a fact that these reps have a much closer relationship to the inner circles of Microsoft, and are usually dealing with higher end, complicated issues that requires consistent good answers for high stakes clients. While our situation may not represent the biggest “fish in the ocean” for Microsoft, it demands a solid answer, which is what we received.

I’m hoping this helps clear up any confusion from others who are on the prowl for this kind of information on Office 365. Rest assured, you can safely import as many domains as you want for the purpose of assigning proper email addresses for your users.

NOTE: For anyone that is curious, Google Apps seemingly supports only a maximum of 600 domains per Google Apps account. This information can be taken with a grain of salt, as the support page that lists this quota is part of a deprecated feature of Google Apps (the Provisioning API) so until Google shows differently, this is the only nugget of information we can go off of. Until then, Office 365 is a better, sure bet for organizations looking to get huge numbers of domains into Office 365 for user accounts and email routing.