AppleScript error -10000 when writing to dropbox directory

Question

I have pasted together an apple script to save email attachments to a directory. Everything works fine, but when I set the output to a dropbox directory, I get an error message:

Result:
error "Mail got an error: To view or change permissions, select the item in the Finder and choose File > Get Info." number -10000

The line producing the error is the one starting with save anAttachment to... in the following script:

tell application "Mail"
    set theMessages to messages of mailbox "Inbox" of account "xxx@yyy.zzz"
    repeat with theMessage in theMessages
        set theOutputFolder to ("/.../Dropbox (Company)/") as string
        repeat with anAttachment in (get mail attachments in theMessage)
            set theAttachmentName to name of anAttachment
            set theSavePath to theOutputFolder & theAttachmentName
            save anAttachment in theSavePath
        end repeat      
    end repeat
end tell

In a non-dropbox directory everything works.

The flags of the dropbox directory are set as follows:

~ $ ls -FLAG -lhd@ Dropbox\ \(Company)                                
drwx------@ 15 username  staff   480B Apr  8 13:52 Dropbox (Company)/
    com.apple.FinderInfo      32B 

I tried to run chmod go+rw on the directory, but that did not help.

GetInfo on the directory yields:

Changing everyone to Read&Write does not help either.

Answer 1

Whilst you get to the bottom of what is preventing you from writing out to folders other than your Downloads folder (which presumably includes subfolders in the Downloads folder), here's a barebones script that should save mail attachments to the folder ~/Downloads/Mail Attachments/.

I've put a filter on the messages being acted upon as retrieving every message in a mailbox is potentially very costly. This retrieves messages from the previous three days:

tell application id "com.apple.SystemEvents" to tell (make new folder ¬
        with properties {name:"~/Downloads/Mail Attachments"}) to set ¬
        directory to the POSIX path


tell application id "com.apple.Mail"
        set _M to a reference to (every message in the inbox whose ¬
                date received > ((my date named 0.0) - 3 * days))

        repeat with A in _M's mail attachments
                set f to the directory & "/" & A's name
                save A in (f as POSIX file)
        end repeat
end tell

You could perhaps add code to migrate the "Mail Attachments" folder from your Downloads folder to your Dropbox folder.