Server :: Replacement Postfix - Getting Intermittant Loss Of Sent Emails

I'm building a replacement postfix email server and I'm getting intermittant loss of sent emails; where: sometimes mail ends up at the recipient (a hotmail address) and sometimes not. Having an offsite relay (or posting directly to the internet) doesnt help either. (Although using hotmail itself as a relay always works despite logged complaints about unchecked ssl certs) Most dissapointingly the log files for the smtp transations are the same for successfully received emails as for the "lost" emails.

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