Normaly the parameter is ok for the current version, but the milter is running under the user clamav and the paramter only works if the milter is running under the user root
QuoteAllowSupplementaryGroups BOOL
Initialize supplementary group access (clamav-milter must be started by root).
Default: no
Send me ssh credentials or a teamviewer session with password per PM
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Problem fixed.. Thread can be closed
Well done!
For future reference, what was the issue? 
Well done!
For future reference, what was the issue?
After disable the parameter
don't restart the milter. Stop and start it
