thanks for the responses.
>>Assuming that is what he meant?
Yup, that's exactly what I meant, RobertoS.
>>Which external mail service does he use?
He uses an e-mail address hosted by 1&1 as part of my website package - the outgoing SMTP server is: auth.smtp.1and1.co.uk As far as I can tell from what he's told me (I haven't actually seen it) the settings he's using are correct (i.e. identical to mine, which work fine on Zen). We've tried changing the outgoing port to 587 (which 1and1 recommend), but it still fails. The general consensus when I asked about this on one of the other forums here
suggested Tiscali are something of a pain for this kinda thing.