Attachment filenames with spaces or colons block sending

[OJFord]

If the attachment filename has a space or a colon (or probably other characters I haven't encountered) in it, sending silently fails, the modal stays open with no error, as if the 'send' button was never clicked.

Should check what the RFC says about this, assuming they're not allowed, need to strip/replace them somehow, or do as spec advises.