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Since July, the E:\Program Files(x86)\Smartertools\SmarterMail\MRS\MailProcessing directory has been filling up with files. To the tune of 20GB. When space became an issue we looked and found that files with the *.TMP extension remained in this directory which I can only guess are temporary files for the handling of attachments on emails. Called a friend and had him check his SM server and he had ZERO files in that directory.
We have ben running Smartermail for 8 years at least and considering that the permissions on that directory is wide open and we never had a problem prior to July 2015, it must be a bug in Smartermail.