Emails going to public Junk inbox after a rehire

Hi All,

I have exchange 2010 with edge server 2010.   Everything is working fine except.   We delete users after the get let go.  Every once inawhile the user gets rehired.  We rebuild the user just like always, but for some reason they cannot receive all the email.  They show up in our company junk folder.

Any Ideas were I can start looking.  

Thanks