SMTP block file extension on EFW2.3

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[funganz]

I enable function block file extension in SMTP proxy.
when I send Email with attach file (.xls) by use encode ISO-2022-JP and file name in Japanese character.
the Endian block my Email, The error log can see as below

amavis[10806]: (10806-01) Blocked BANNED (application/vnd.ms-excel,.doc,\e$B#K#J#T\e(B11\e$B<!\e(BBRG\e$B7j@{HW2C9)\e(B-1\e$B!J\e(B240) 2\e$B2sL\\\e(B.xls,=?ISO-2022-JP?B?GyRCI0sjSiNUGyhCMTEbJEI8IRsoQkJSRxskQjdqQHtIVzJDOSkbKEItMQ==?= =?ISO-2022-JP?B?GyRCIUobKEIyNDApIDIbJEIyc0xcGyhCLnhscw==?=),

but in block file extension I didn't choose .xls file
I also test again with encode UTF-8 in the same Email, the result can send normally

but my company policy need to use encode ISO-2022-JP,

How can I do?

Thank you for you help