The title above is quite long, but exactly to the point - I found myself unsure how to add a resource room in Office 365 for Exchange online because it was set up by previous employees and hadn't been done since then. Then I needed to add it to the Rooms List. I will walk you through my process of how I created a room and added it to a room list. This was also done in a hybrid environment (Exchange Online and Exchange 2013).

Create User Account

The first step is to create a regular AD user account. I created it in Active Directory User and Computers. You will not need to know the password, so set it to something crazy long and forget it. Be sure to set the password to never expires. And after all of this is said and done, we will disable the account for security.

I filled out Display Name, Telephone Number and Password Never Expires.

Setup The Account

Because I am in a Hybrid Exchange, I have to run the following command on my local Exchange server. You likely just need to ignore this.

Enable-Remotemailbox "hrmeetingroom@company.com" -RemoteRoutingAddress "hrmeetingroom@company.mail.onmicrosoft.com"

Sync Active Directory

Sync Active Directory with Azure AD Connect.

Convert to a Resource Room

This is where the fun starts. This step is to actually convert the user's mailbox to a resource room. You have to do this via PowerShell as there is no GUI way of doing it that I could find.

# Get your Office 365 credentials
$UserCredential = Get-Credential
Start remote PowerShell
$Session = New-PSSession -ConfigurationName Microsoft.Exchange -ConnectionUri https://outlook.office365.com/powershell-liveid/ -Credential $UserCredential -Authentication Basic -AllowRedirection
#Import the remote session

Import-PSSession $Session
#Convert to a Resource Room

Set-Mailbox ""<username> -Type Room

Wait a minute or two.. and bam.. You just created a room. From there, I log into the Office 365 Portal and customize the room to my liking.

Add The Room To A Room List


With your same PowerShell session where you are already connected you will manipulate the rooms list. Rooms list are a type of Distribution Group with the room tag added to it in Office 365. As far as I know of, there is currently no way to manipulate these in the admin portal. Below are some commands you will find useful for this:

List Room Lists in your tenant
Get-DistributionGroup | Where {$_.RecipientTypeDetails -eq "RoomList"} | Format-Table DisplayName,Identity,PrimarySmtpAddress
List All Resource Room Mailboxes
Get-Mailbox | Where-Object {$_.RecipientTypeDetails -eq "RoomMailbox"} | Format-Table DisplayName,Identity,PrimarySmtpAddress
List Rooms in a Resource Room List
Get-DistributionGroupMember -Identity <RoomList>@<tenant>.onmicrosoft.com
Here is what you will use to add the room to the Room list in Office 365:
Add-DistributionGroupMember -Identity <roomlist>@<tenant>.onmicrosoft.com -Member <roomusername>
After doing this, I checked my work by listing the rooms in the Room list again and then you are DONE! You have created a room, customized it, and added it to the room list.
The last part is waiting for the Global Address List to be updated and wait for everyone's Outlook to update to the GAL. It can be accessed from the Room List and added to a user's calendar right away though.
Please let me know in the comments if this helps you or if you know any tweaks to make it easier for you! 
Originally posted at  https://moreabout.tech/creating-rooms-in-office-365-exchange-online-and-add-to-rooms-list/