There isn't a way to generate a "formal" report on this - but, you can tailor your own with using 'grep' on the CLI of your appliance... choose your mail_logs and use the key word "PXE encryption filter"
Ex.
<snip>
Enter the number of the log you wish to grep.
[]> 17
Enter the regular expression to grep.
[]> PXE encryption filter
Do you want this search to be case insensitive? [Y]>
Do you want to tail the logs? [N]>
Do you want to paginate the output? [N]>
Define file selection pattern.
[]>
Mon Apr 14 10:09:17 2014 Info: MID 72 was generated based on MID 71 by PXE encryption filter '_CRES_encrypt'
Mon Apr 14 12:08:58 2014 Info: MID 91 was generated based on MID 90 by PXE encryption filter 'SB_SSN'
Mon Apr 14 12:32:01 2014 Info: MID 94 was generated based on MID 93 by PXE encryption filter '_CRES_encrypt'
Tue Apr 15 12:04:35 2014 Info: MID 103 was generated based on MID 102 by PXE encryption filter '_CRES_encrypt'
Tue Apr 15 16:07:24 2014 Info: MID 106 was generated based on MID 105 by PXE encryption filter 'Default Action'
Tue Apr 15 16:10:50 2014 Info: MID 109 was generated based on MID 108 by PXE encryption filter '_CRES_encrypt'
Wed Apr 16 10:57:22 2014 Info: MID 113 was generated based on MID 112 by PXE encryption filter 'Default Action'
Wed Apr 16 11:00:12 2014 Info: MID 116 was generated based on MID 115 by PXE encryption filter 'Default Action'
So - you can see that 8 messages were in mail_logs that went through the associated encryption filters. If you export your mail_logs to a syslog server - and have full grep/sed/awk capabilities, you could then just do a count based on the grep string you are after to get the #'s easier.
-Robert
