Microsoft published an important hotfix for .NET 4.5 earlier this year. It wasn’t picked up on by many, therefor a quick write up on the matter.

Since Exchange 2013 is built on top of .NET 4.5, it is recommended to install the hotfix on all Exchange 2013 Mailbox and Multi-Role servers. The hotfix will reduce the memory consumption of the store worker processes.

If you’re using Windows Server 2008 R2, the hotfix is KB2803754 and can be requested here; when using Windows Server 2012 the hotfix is KB2803755 which can be requested here.

After installing the hotfix, you need to do one of the following things:

• Set the following registry key:
  HKLM\Software\Microsoft\.NETFramework\DisableRetStructPinning=1 (REG_DWORD)
• Set the COMPLUS_DisableRetStructPinning environment variable to 1

I’d prefer the first option. Note that you need to restart the server for the change to become effective.

Thanks to Tony Redmond for the heads up.