What are some considerations for a public folders migration?

A public folders migration from one version of Exchange to another can tax the skills of an experienced administrator -- but there's another level of complexity when cloud enters the mix.

A session at last week's Virtualization Technology Users Group event in Foxborough, Mass. detailed the nuances of Office 365 subscription offerings and the migration challenges administrators face. Microsoft offers a la carte choices for companies that wish to sign up for a single cloud service, such as Exchange Online, and move the messaging platform into the cloud, said Michael Shaw, a solution architect for Office 365 at Whalley Computer Associates in Southwick, Mass., in his presentation.

Microsoft offers newer collaboration services in Office 365, but some IT departments cling to one holdover that the company cannot extinguish -- public folders. This popular feature, in 1996 with Exchange 4.0, gives users a shared location to store documents, contacts and calendars.

For companies on Exchange 2013/2016, Microsoft did not offer a way to move "modern" public folders -- called "public folder mailboxes" after an architecture change in Exchange 2013 -- to Office 365 until March 2017. Prior to that, many organizations either developed their own public folders migration process, used a third-party tool or brought in experts to help with the transition.

Organizations that want to use existing public folders after a switch from on-premises Exchange to Office 365 should be aware of the proper sequence to avoid issues with a public folders migration, Shaw said.

Most importantly, public folders should migrate over last. That's because mailboxes in Office 365 can access a public folder that is on premises, but a mailbox that is on premises cannot access public folders in the cloud, Shaw said.

" can always access old, but old can't access ," he said.

IT admins should keep in mind, however, that Microsoft dissuades customers from using public folders for document use due to potential issues when multiple people try to work on the same file. Instead, the company steers Office 365 shops to SharePoint Online for document collaboration, and the Groups service for shared calendars and mobile device access.

In another attempt to prevent public folders migration to Office 365, Microsoft caps public folder mailboxes in Exchange Online at 1,000. They also come with a limit of 50 GB per mailbox in the lower subscription levels and a 100 GB quota in the higher E3 and E5 tiers. Public folder storage cannot exceed 50 TB.

Still, support for public folders has no foreseeable end despite Microsoft's efforts to eradicate the feature. Microsoft did not include public folders in Exchange Server 2007, but reintroduced it in a service pack after significant outcry from customers, Shaw said. Similarly, there was no support for public folders when Microsoft introduced Office 365 in 2011, but it later buckled to customer demand.