Policy
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.
Pack Microsoft Office
Category Microsoft Outlook 2016 / MIME to MAPI Conversion
Policy ID
c618db444fbd Internal name
L_ChangethelimitMIMEheaders Registry
Copy registry mappings
HKCU\software\policies\microsoft\office\16.0\outlook\options\mail\mimeheadersPolicy notes
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.