Re: [Trisquel-users] Mail Disappears From Inbox!

[jason]

If it only happens after checking mail from your proprietary email program  
perhaps that seems to point the finger in that direction. Before you say "but  
I can still see them in the proprietary program", keep in mind that the  
messages that appear in that proprietary program don't necessarily have to  
even exist on the mail server anymore.

Other people using proprietary software seem to have similar problems, like  
https://discussions.apple.com/thread/8231116