On the Location document, the field "Format for messages addressed to Internet address" now contains the default value of "MIME format." This change was effective in Notes 5.0.10.
In the Notes 5 documentation, the topic "Using MIME or Rich Text Format in the mail form" contains incorrect information. MIME format is now the default so the procedure does not need to be completed in order to use MIME; you would need to use that procedure to switch to Rich Text Formatting. In Step 3 of that procedure, to switch from MIME to RTF, choose Rich Text Formatting.