Hi,
The thing is that fetchmail will not send a delete message to the server where you fetch your email, unless it gets a delivery OK from wherever you want to store it. However, you might want to check this page. It contains information how to tweak fetchmail so that it will also delete emails that cause errors on your local MTA.
Again this is advanced non standard operation that requires console access. And yes I can do it and you can do it, but we both need to be made aware of the fact that we should do it, in response to someone having changed something that causes our systems to behave badly. Like an external virus. Tweaking fetchmail to also delete undeliverable emails does seem to be the better choice though over altering the message limit on postfix and should not require reconfiguring if your ISP unilaterally decides to increase the message size limit once more (or you switch to another email provider).
Also consider this: for every 552 message you sent that other party, you downloaded some 36MB that went straight to the bin. Consequently, if you pay your internet connection by the MB this would be a rather expensive joke being pulled on you.
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