It’s been a while since I’ve broken out PowerShell to solve a problem, but a scenario came up where I thought I could automate something I needed to do – look up a bunch of Microsoft 365 Tenant IDs based on domain names. Here’s how I tackled it:

First, I actually had a list of email addresses and just wanted the domain of each one. The list was in Excel so that’s easy enough – using the Text to Columns feature I selected the data, used the ‘Delimited’ option under Original data type then pressed Next:

Then on the next step, changed the Delimiters from the default ‘Tab’ to ‘Other’ and put the @ symbol on, and as you can see in the Data preview it takes the alias off the email address for the first column, and leaves the domain in the second:

Clicking ‘Finish’ gave me a column full of domains. From this, I created a header for each row (alias and domain):

And then in Excel went to File > Save As > and called the file ‘addresses’ while picking CSV from the dropdown:

Easy enough. From here, I knew I’d need to feed this data into PowerShell using the Import-CSV command, but first I wanted to work out what the one liner command was to get a M365 Tenant ID…. except I couldn’t find one. All the examples were how to find your own M365 Tenant ID after authenticating. I knew it was public and easily accessible since sites like https://whatismytenantid.com/ work great but only accept one domain at a time.

I ended up finding a Function written by Daniel Bradley which was fairly simple and using an API, with the core of it being this one line:

Invoke-RestMethod -UseBasicParsing -Uri "https://odc.officeapps.live.com/odc/v2.1/federationprovider?domain=$domain"

Swapping the $domain variable with an actual domain and piping to just selecting tenantid

Invoke-RestMethod -UseBasicParsing -Uri "https://odc.officeapps.live.com/odc/v2.1/federationprovider?domain=microsoft.com" | select tenantid

tenantId
--------
72f988bf-86f1-41af-91ab-2d7cd011db47

Alright, we should be able to put this all together. Set the $file variable as the imported CSV file, then for each domain record run the Invoke-RestMethod command using the current $record.

Except that didn’t work because I forgot the $record is the entire object and not just the domain membertype. To specify that, we just use $record.domain so the pure domain is used.

Except that didn’t work either and I don’t know why. Instead, I just made a new variable from the $record.domain and called that $newdomain, then referenced THAT in the Invoke-Restmethod line.

That did work, so I could then echo out the results of both the current $newdomain variable, and the newly looked up $result and again specifying the membertype of tenantid (as a bunch of other info gets looked up with that command).

I also then wanted to export this data back out to a new CSV, in this case one called ‘myfile.csv’. Again, I have to work around membertypes so just make a new variable containing the single tenantid line, and use the >> operator to create/append to a file:

$file = import-csv c:\temp\addresses.csv

foreach ($record in $file){
        $newdomain = $record.domain
    $result = Invoke-RestMethod -UseBasicParsing -Uri "https://odc.officeapps.live.com/odc/v2.1/federationprovider?domain=$newdomain"
$newtenantid= $result.tenantid
echo $newdomain $result.tenantid
"$newdomain,$newtenantid" >> c:\temp\myfile.csv
}

Works perfectly and I end up with a CSV that has a column of domains, and a column of Tenant IDs. If a domain had no Tenant ID then that value will be blank.

I’m sure this could be written better, but for quick occasional tasks for yourself, you just need something that works.