White listed emails going into spam folder

[#1]

for some time a number of white listed emails that are not spam finish up in the spam folder. I have marked these as not spam and re-entered the email address in the white list but they still finish up in  the spam folder. The senders that frequently finish up in the spam folder are emails from Which, Alaxander work wear and Richer Sounds although not all get the spam treatment some get through.
Can any one help?

[#2]

Are the addresses you've entered in the whitelist taken from the 'return path' header or 'from' header? The former ones need to be used for whitelisting to work. It's usually easier to enter just the sender's domain, everything after the @.

[#3]

I have used the from header. I will try the return path using the domain instead of the full address and see if it works.
Thank you for your advice.