The CONVERTER_LOG_LEVEL setting in NOTES.INI can suppress the logging of MIME conversion to LOG.NSF.
In Lotus Domino, when a message is converted to (or from) MIME, the following message displays on the Domino console and is written to LOG.NSF:
"Begin CD to MIME Conversion (Process: Router )"
The following values are valid for this setting:
10 - log Fatal and Error events
20 - log Fatal, Error, Warning, Info Terse (this is the default)
30 - log Fatal, Error, Warning, Info Terse, and Info Verbose
40 - log Fatal, Error, Warning, Info Terse, Info Verbose, and Info More Verbose
When absent or set to 20, the default behavior is to log Fatal, Error, Warning, Info Terse events.
Set this option to 10 to reduce LOG.NSF activity.
The router must be restarted for the parameter to take effect.
How to disable logging when a message is converted
Domino Configuration Tuner:
This setting is included in the DCT catalog of best practices as of Domino 8.5