[exim] malformed addresses on the commandline

I'm mailing multiple recipients on the commandline like this:

cat msg | exim a@???, b@???

and was slightly surprised to find that if one recipient is *syntactically*
malformed e.g:

cat msg | exim a@???, b@???, c@bad_com

then NONE of the recipients get the message. Yes, this is made clear in
the resulting bounce message, which says "The message has not been
delivered to any recipients.". This was a surprise, and a slight problem
since I can't guarantee the list of addresses I have to mail will always
be syntactically valid.

By contrast, if the recipients are supplied via the headers like:

Bcc: a@???, b@???, c@bad_com

and exim is invoked like:

cat msg | exim -t

then the good recipients DO get the message, and the resulting bounce
message says "c@bad_com - This address has been ignored. The other
addresses in the message were syntactically valid and have been passed on
for an attempt at delivery".

So I seem to have a workaround. But am curious if I'm missing something
obvious, and/or if there's a section of the manual that discusses this issue.

Chris

--
Chris Edwards, Glasgow University Computing Service