Hi, is this happening on a webmail site where you are reading your email in Firefox, or in Thunderbird?

I am using Firefox with Yahoo (att) email. Thanks.

Unless you have an add-on that manipulates your mailbox, or another mail program accessing your mailbox that is doing it, this must be caused by some setting in the site. It is difficult to imagine Yahoo would have a setting for "throw every new email message into the trash." Maybe there is an errant mail processing rule, if Yahoo has those??