emails do NOT work correctly

emails do NOT work correctly

I have emails going into my clients junk mail, emails not being received at all by clients, emails not coming in to my mailbox, and emails taking a long time to show up in the mailbox. I also changed the password for my email address and when we updated it in zoho there was an error and it kept saying password incorrect (yes we put in the correct password).
Would appreciate some enlightenment on why this is all happening as I am beginning to grow tired of the issues with this system.