[Evolution] why do some of my emails delete themselves??

[ARLENE B <arlene baker99 gmail com>]

I have been a long-time Thunderbird user, but for some reason, it
doesn't want to allow use for gmail, so any new machines I have had, I
had to switch. Now, I like evolution pretty well, except there are
times when an email just disappears, without my deleting it. This is
very annoying. How can I stop it? And CTL+Z does not 'undo' the
deletion. How to do Undo something? Also how can I stop this auto
delete from happening. 

I would also like to see the color labeling as Thunderbird does when
you tag an email. Is this possible?
Thank you!
Arlene in Tucson