The sender concerned wasn't appearing in her spam, and I couldn't find the address concerned in the filtering rules, (we're talking webmail here), but turning off the filtering enabled the contributors email to get through.
Perhaps it's somethign similar. See if you can turn off spam filtering.
Even if you dont want to leave it like that it might isolate the problem.
Thank you for the replies. Sorry but I have been away for a few days.
I am not very email literate and I don't know exactly what a hotmail account is. My account is with BT Yahoo Mail and is a "btinternet.com" address. I don't know what program I am using to receive the mail as I just log on to email from my Yahoo home page. Last week I went into the "bulk folder options" and in "pop access & forwarding" I ticked the box "I want to receive messages including those that spamguard thinks are spam". This has made no difference and I still am not receiving my friend's mail. I am however receiving other mail and spam.