Sorry Updating it late . I have fix this Issue .
Issue : As the Name of the Attachment in email is in different language ,its setting UTF-8 unicode of that particular language while setting the Name of the Attachment in EmailHandler.Java file .this is the reason the name is getting Corrupted .
I have modified the EmailHandler.java to decode the type of language and preserve same name after converting email in Mendix . Below is the Piece of code I have Added to fix this is :
attach.setName(MimeUtility.decodeText(bodyPart.getFileName()));