I mostly send untracked large letters internationally, at about 15% of my total sales.  I have only had 1 international item go missing in the last 6 months (New Zealand) so I have no concerns. BUT you should avoid some countries with a high strikerate of postal problems (for me I do not ship to Canada Central & South America and a few more places). Vast majority of my international sales are to USA and England and I find their postal services very reliable.