When you have multiple top domains you want to use on the same O365 tenant.
For example: Sem@msitpros.com, Neo@msitpros.net and Mr.email@example.com
Remember to add the -SupportMutipleDomain parameter when you convert your domains.
Convert-MsolDomainToFederated -DomainName msitpros.com
NB: If you run ADFS 2.0 (2008R2 or older) you will need to install rollup 1 update for ADFS.
However I do recommend to use the latest and greatest ADFS 3.0 (2012 R2)
If you do not specify this parameter on the first domain that is converted you will not be able to convert the others.
now if you like me did not know this and tried to convert the next domain you will receive this error:
The federation service identifier specified in the Active Directory Federation Services 2.0 server is already in use. (even though I use ADFS 3.0)
If you then try to use the SupportMultipleDomain parameter on the second domain you will get this error:
The switch parameter SupportMultipleDomain is not supported here
But don’t worry there is still hope.
What you need is to delete the trust relationship in the ADFS console and you are able to start from scratch.
This time remember to use the -Supportmultipledomain parameter on all the domains you want to federate.