Some Cox emails not forwarding to gmail

I forward all of my cox e-mails to gmail.  All of them are forwarding successfully and being received by my gmail except for emails from one particular Cox sender, and one particular aol sender.  I have created filters in gmail to allow them through, but they are still not coming.  I have resorted to checking Cox webmail regularly to make sure I don't miss any incoming e-mail.  So, I am unable to tell if Cox isn't forwarding them, or if gmail isn't accepting them. Any suggestions appreciated.