This gap has been asked about in public, on the record, since 2012.

Room Mailbox for a room that can be divided

An event-hosting room divisible by a partition, considering three mailboxes: the Whole room, Side A, and Side B. Someone could book Side A, then someone else books the Whole room, with nothing to stop the conflict.

"You'd have to find some way to tier that." Limey, Best Answer

Limey's advice: drop the combined "Whole" room resource entirely and require booking both sides for the full space. The oldest documented instance of this exact question found in this research.

Combined Conference Rooms in Exchange

A large conference room splits into two smaller ones. The original poster asked whether Exchange could auto-book both smaller rooms whenever the large room was booked.

"Not possible." Corey7569

The original poster's own closing reply accepted this as the practical answer.

Booking 1 meeting room to book 2

The same question this page exists to answer: does Exchange or Microsoft 365 support automatically blocking a second room when a first is booked.

"Not by default. There might be some third-party tools that allow for resource dependencies." VasilMichev, Microsoft MVP

Booking Divisible Meeting Rooms

A room splitting into three parts, adjacent pairs only. The poster was migrating off a custom booking system that already handled divisible rooms and hoped Exchange could keep that capability.

Exchange Room Lists are "just distribution groups for organizing, not booking logic." bluesoul

The original poster explicitly preferred a built-in solution over a third-party one.

Resource mailbox for room that can be devided

A request for three listed rooms, Room A, Room B, and Room AB combined, where booking the whole room while a smaller room was already taken would auto-decline the invite.

"There's no related policies/rules in Exchange to achieve your request." kelvindeng

The fallback discussed in the thread: keep two separate rooms and rely on a written policy asking staff to request both when they need the full space.

Outlook Room Resources. Joint Meeting Rooms

A new office building with a retractable wall joining two rooms into one large space. The poster wanted booking the large room to also populate both smaller rooms' calendars.

"The best option is to have separate bookings." michev

Split meeting room booking

One large room splits into two smaller ones. The original poster needed booking Room 1 to automatically block Rooms 2 and 3.

"In essence you reached the limits of Exchange room booking." Harald_Steindl, Iron Contributor

Only third-party layers built on top of Exchange were said to handle this kind of dependency.

How to create 2 conference rooms that can be combined into 1 large room?

Two new Teams-enabled conference rooms with a collapsible wall between them. The poster couldn't find documentation on building this configuration in Exchange 365.

"There's no easy way." joeykins82

The thread lays out two paths: a MailTip-based policy telling users to book both rooms, or a custom build polling the Graph API to keep separate mailboxes in sync.

Nested Room resources

Two small rooms combine into one large room behind a physical divider, mirrored in Exchange as three separate room resources. Booking the small room doesn't block or notify the large-room resource, so double bookings happen in practice.

"There is no such thing as nested room resources." Dillon Silzer, Microsoft MVP & Volunteer Moderator · confirmed by Jame Xu-MSFT, Microsoft staff

The suggested workaround, a mail flow rule, was assessed by the original poster as impractical and prone to mail loops.

Multiroom Exchange Room Resource

The poster's own framing of what they needed:

"The rooms should manage themselves." MiThm2495, original poster

A contributor suggested Exchange booking policies configured via PowerShell. The poster's own follow-up in the thread indicates that path didn't meet the automatic-dependency requirement.

Room List or Room Group to book multiple rooms at once

The same ask again: group two room mailboxes so booking the group reserves both. No official reply at time of writing. Included here as a further independent instance of the question, not as an additional confirmation.