set theOutputFolder to "Macintosh HD:Users:Mein Name:Desktop:"

tell application "Mail"
    try
        set selectedMessages to selection
        if selectedMessages is not {} then
            repeat with thisMessage in selectedMessages
                set theAttachments to every mail attachment of thisMessage
                repeat with a from 1 to length of theAttachments
                    set theAttachment to item a of theAttachments
                    try
                        set theAttachmentName to name of theAttachment
                        set theSavePath to theOutputFolder & theAttachmentName
                        save theAttachment in theSavePath
                    end try
                end repeat
            end repeat
        end if
    end try
end tell