some contacts in my group are getting my emails in their work mailbox,

Now I have discovered that some contacts in my group are getting my emails in their work mailbox, not their home or main email.  This is a problem, as most employers frown on employees receiving unrelated emails in your work email.  So far the only solution I've come up with is to click on the plus and check every time I send something out to be sure the message goes to home emails and not work.  I always find several.  Why would hotmail decide to use work emails instead of home emails when they are plainly labeled "work" on the contact's page?