Webmail does NOT automatically delete the Trash folder contents.
The probable answer is that your android email app is issuing a command to delete all.
That linked thread has been superseded, the webmail trash folder does now automatically delete anything that has been in it for more that 30 days. This happens around the beginning of each month.
I would agree that some setting in the android email app is causing the total deletion.
_________________________________________________________ Graham I am a VM customer. There are no guarantees that my advice will work. To say thanks click the kudos thumb. If I have solved your problem please click the helpful answer button.