evolution refusing to send email with attachment

[michael <linux@networkingnewsletter.org.uk>]

I've not had too much trouble with evolution (email client) until just
now when it was complaining:

Error while performing operation.
DATA command failed: Requested action not taken: mailbox unavailable.

(but there's on missing mailbox!)... finally tracked this down to having
the following as an attachment with filename suffix .csh (the below
being a simple example of what fails)

anybody else seen this problem or know solution?

michael@ratty:/tmp$ cat wtf2.csh
#!/bin/csh -f