IMO, the two previous links were off-topic to what the OP is asking, but this is.

http://blogs.igalia.com/svillar/2009...cture-support/
(Dec 16) "With this new feature, we can download every MIME part one by one, and thus saving you time, disk space and specially if you’re using a mobile device like N900, money in your GPRS connections. Do you want to read only the body? No problem we’ll show you that you have some attachments but we won’t download them until you request us to do so. Do you want to forward the full message? No problem, we properly detect that and include the full original message whether or not it was completely downloaded before.

This will most likely be included in the next N900 software update that will be eventually delivered by Nokia."