Syrte
·Functioning self-stick envelopes are practically impossible to unfasten without leaving obvious evidence of tampering. If this one looked like it had simply come undone, then I'll wager that's probably what happened. Those things do have a limited shelf life, after which they tend to become self-nonstick.
OK. So I should not be suggesting people secure their shipments, because envelopes are secure as they are? is that the overall point you're trying to get across?

