[bitfolk] Emails not delivered to btinternet.com addresses

We are having problems delivering mail to @btinternet.com addresses from our VPS running Postfix on Debian Lenny. From the limited information I found on Google it seems likely that the e-mails are being delivered but then moved to the users webmail spam folder. In my case the (two) users are not aware that they have webmail, but I believe they do (provided by Yahoo?). Here's a mail.log file extract (user name edited): Dec 28 17:28:44 vs1 amavis[9066]: (09066-08) Passed CLEAN, [86.0.209.51] [86.0.209.51] <martin(a)jset.net> -> <xyz(a)btinternet.com>om>, Message-ID: <4D1A1E26.2060901(a)jset.net>et>, mail_id: BQJb5C4gVigN, Hits: -5, size: 6507007, queued_as: 41CD6E2F7, 1372 ms Dec 28 17:28:44 vs1 postfix/smtp[9732]: 69772E2F3: to=<xyz(a)btinternet.com>om>, relay=127.0.0.1[127.0.0.1]:10024, delay=74, delays=73/0/0/1.4, dsn=2.0.0, status=sent (250 2.0.0 Ok, id=09066-08, from MTA([127.0.0.1]:10025): 250 2.0.0 Ok: queued as 41CD6E2F7) Dec 28 17:28:44 vs1 postfix/qmgr[5081]: 69772E2F3: removed We use the same server for business and personal e-mails and the only problem I'm aware of is with @btinternet.com addresses. Thunderbird on the client machine is using the vs1 SMPT server with hostname jset.net. Emails are delivered if we use our broadband provider's SMPT server (but they are slow and frequently time out and not suitable for mobile working). Any suggestions/configuration changes to debug this would be welcome. Regards, Martin