Outlook truoble with aruba

Hi

we just buy bit defender as our antivirus and now we stop reciving mail. We use outlook2021 and have as provider aruba. as soon as we open it it signal that doens't consider aruba certiface affidable, i have try to install the certificate but nothing changes.

we are able to send but not to recive

it's happening to me and my friend, on both machine outllok send but it's not reciving and it's not giving any error on the outlook side.

what can we do to solve the problem? thanks a lot