Incoming email rejection

[#1]

Plusnet is rejecting emails from a sender as suspected spam.  Fortunately I have been able to receive the emails at another email address, but my plusnet address is my default, and I want to be able to receive emails from the sender there.  Any ideas as to how I can get Plusnet to accept an email, rather than rejecting it?

[#2]

Check and adjust  your Spam settings. Login to your account, select Manage my mailboxes from the Manage account tab. The select the Spam tab and review your settings