Change the limit for the number of MIME headers

By default, the limit is 20000 for the number of MIME headers when an e-mail message is converted from MIME to MAPI. The number can be set to any positive integer. This helps prevent scenarios in which Outlook hangs while attempting conversion.

Supported on: At least Windows Vista

Registry Pathsoftware\policies\microsoft\office\14.0\outlook\options\mail
Value Namemimeheaders
Default Value20000
Min Value
Max Value99999


Administrative Templates (Users)