Outlook for Mac

When I'm on my phone, I don't always see all my emails.  I use it numerous times a day and usually at least once a day, I check in on my computer a mac.  Lately, it has been acting unusual and as you can see from the attached, it now says NOT SECURE and when I try to open an email that does pop up, I get this notice.  Not all the emails load.  If I open junk mail, to the left it says 400 but when I click on it, it says junk mail is empty.  This is miserable!!  Trying to get a real person to help me is impossible.  I am 76 and this is very unnerving.  I have always used Safari as my browser and I don't want to change.  HELP!!