cubicweb #1450617 mail notification error with multiple addresses [rejected]

Seen in the extranet-jpl logs (anonymized):

2011-01-26 15:14:39 - (cubicweb.configuration) ERROR: error sending mail to [u"[u'', u'']"] ({u"[u'', u'']": (501, '5.1.3 Bad recipient address syntax')})
Traceback (most recent call last):
 File "/usr/lib/python2.6/dist-packages/cubicweb/", line 1176, in sendmails
   smtp.sendmail(heloaddr, recipients, msg.as_string())
 File "/usr/lib/python2.6/", line 709, in sendmail
   raise SMTPRecipientsRefused(senderrs)
SMTPRecipientsRefused: {u"[u'', u'']": (501, '5.1.3 Bad recipient address syntax')}
done in<not specified>
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