Apple Mail deletes messages automatically when cursor hovers

On both my iMac desktop (using external trackpad) and macBook Air (using built in trackpad), when reviewing emails (in Apple's Mail program):

If I delete or archive a message and don't move the cursor out of the menu bar, after a brief moment the program executes that action. That is, if I deleted the previous message, leave the cursor hovering on the menu bar, Mail will delete the next message as I am reading it in the preview pane, even if I haven't clicked the mouse.

It is also possible that leaving my finger resting on the trackpad is doing this, even if I did NOT intend to click. But I cannot find a sensitivity setting for the trackpad that might make it less easily triggered.