It was great to see the EHLO blog informing the Exchange community that work is progressing to increase the scalability of modern public folders and raise the somewhat pathetic limits revealed last March. As you’ll recall, the old limits were 10,000 public folders in the hierarchy and 100 public folder mailboxes.

To be fair to the public folder team, they walked into the lion’s den at the Microsoft Exchange Conference (MEC) when they faced an unhappy crowd at the “Unplugged” session for public folders and site mailboxes. Not that site mailboxes were discussed much at that session, which probably reflects the current level of usage for site mailboxes in the wild.

In any case, public folders program manager Kanika Ramiji kept calm and noted the three issues that customers wanted Microsoft to deal with in modern public folders. The first is scalability, and that’s being worked on right now. It’s good that the limit will be raised soon to allow Office 365 tenants to use 100,000 public folders. It’s even better that the scalability work will continue and show up in Exchange 2013 CU6 (due in less than a quarter now) and that the final goal is to support more than 1 million public folders.

As noted in the blog post, scalability improvements take time because they are complex. Microsoft has already enjoyed some robust customer feedback over the initial limits; they won’t want to experience the same reaction if modern public folders fail to scale properly again.

But you’ll notice that nothing was said in the blog post about raising the limit of 100 public folder mailboxes within an organization. On the surface, this shouldn’t be a huge issue as a public folder mailbox is able to hold an awful lot of information.

Office 365 limits public folder mailboxes to 50GB and automatically splits public folders across new mailboxes when that threshold is reached. On-premises deployments can support public folder mailboxes of up to 100GB. However, this is a “soft” limit and a mailbox won’t stop working if it is forced to hold 100.1GB. Rather, it’s a matter of how supportable, reliable, and performant mailboxes are when they hold very large amounts of data.

I imagine that the need to restrict hierarchy updates is the reason why Microsoft is holding to 100 mailboxes for now. The primary public folder mailbox handles all updates to the hierarchy and then fans out updates to all of the other mailboxes, each of which holds a secondary read-only copy of the hierarchy. Updates are very smooth when servers are connected with high-speed reliable networks, but it’s easy to see how things might not work so well if Exchange had to process public folder hierarchy updates across thousands of mailboxes distributed in databases around a large network where some of the links aren’t quite as good as you’d like.

So you could be faced with the need to stuff a one million folder deployment into 100 public folder mailboxes. Hopefully everything will fit in 10TB. If not, it’s time to take out the pruning scissors before you start the migration process to move old public folders to Exchange 2013.

The other issues identified at MEC were lack of support for public folders holding calendar and contacts items in Outlook Web App (OWA) and the lack of reporting and management tools for public folders. The EHLO post says that the public folder team have the OWA limitation on their radar and will get to it after the scalability issues are fixed. If the scalability fixes come to on-premises customers in Exchange 2013 CU6, you can assume that it will take one or two further updates before support for calendar and contacts folders show up.

No word is available on what might or might not happen for reporting and management tools. Given the sad history of neglect on this front for public folders and other elements in Exchange, it would come as no surprise if progress is slow here. But we live in hope!

Follow Tony @12Knocksinna