WLM 2012 keeps putting deleted emails back into inbox…why???

this has happened three times alone this morning, 2/10/19.  i'll delete 300+ emails, some almost two weeks old, then 5-10 minutes later they reappear.  again, this has happened three times this morning alone.  it has happened periodically, maybe once or twice a month, over the past year or so, and was nothing more than an annoyance, but three times in a matter of an hour?  am i missing something?  yes, i've already tried to search online to solve the problem.  i have att as my provider.  i am running the latest version of windows, whatever that may be at this point.  i have only one account associated with my email.  yes, i do know that WLM 2012 is antiquated, but i cannot get outlook to work for some reason on my machine.  i will be changing internet providers in a few weeks and i hope that solves the problem, from att to spectrum.  anything else???  any help would be sincerely appreciated as this is getting very, very tiresome.

thank you for your time.