MJ, I am not sure why using a USA proxy creates a security issue? The data is encrypted. I don't think proxy-ies are using highly specialized man-in-the-middle attacks.
Just to provide a different viewpoint, I use a mailing service based in the USA. They receive all of my mail, and send me a picture of the front of any mail I receive on the same day. I can have the mail scanned or forwarded. This is also my official address and it is not a P.O. Box. They can also receive registered mail, packages, etc. This is the address on my USA driver's license, also.
My total cost for this is only around $100 per year, including a couple of forwardings to a USA address (when I am visiting). But you can have the mail forwarded anywhere.
So when I got mail from the IRS about an audit when I was overseas, I was able to request a scan ($3.00, I think) and it was available as a PDF file less than 24 hours later. With scans there is a slight chance of identity theft by the person doing the scanning, but the whole reputation of the company depends on the integrity of the mail.
After living abroad for 5 years, I have no use for snail mail really, except as a legal address which seems to be required for various things (just like a USA phone number, which I also maintain). I do usually use the paper docs as a convenience for tax preparation (although not required) and use the paper year end statements for financial archives.