I have pop accounts set up for my business. Ever since the last Thunderbird upgrade, I've been seeing messages download and then immediately disappear. Some of these have been critical things that I needed to get, and I've had to ask the sender to repeatedly re-send them before they stopped disappearing as soon as they came in. They have been from a wide variety of sources, including the US government, so it's not a problem with the sender. I've used Thunderbird for all the years that it's been available, without any problems ever, until this began. Please fix it, whatever it is!