You cannot edit the message subject through Outlook

Original KB number:   4022843

Symptoms

When you open a message in Outlook and select the subject, the text cursor does not appear, making it impossible to edit the subject of the message.

Cause

This issue occurs when the message header is collapsed.

Outlook 2013 Service Pack 1 and newer versions can collapse the message header to compact the size of the message.

Resolution

Expand the Outlook Infobar by selecting in the lower right arrow to expand the header for editing.

Expand the Outlook Infobar

More information

In Outlook 2013, the default behavior is the expanded header while Outlook 2016 the default behavior is collapsed header. When the header is collapsed, the subject field is NOT editable.

We can change the default behavior of the Outlook to always expand the header using the registry key below:

HKEY_CURRENT_USER\​SOFTWARE\​Policies\​Microsoft\​Office\​16.0\​outlook\​options\​mail
DWORD: MinimalHeaderOn
Value: 0

0 = expanded
1 = collapsed