Why are some of my favorite sender’s list being sent into my junk and archive folders?

Most emails I’ve been receiving from my business partners are either ending up in my junk mail or archive folder. I email these individuals daily and they are on my favorites. Oddly, all of my emails are going into their spam folders too? This cannot be coincidental and certain that someone has sent some kind of spyware or Trojan into our accounts. Any recommendations on finding out what we can do about this situation.