Incoming email not spam but when forwarded it is spam ???

[#1]

Got an email from compare the market with insurance quotes.  This is a legit email and not spam.  The email arrived in inbox no problem.
Went to forward it to partner and got the 'you are sending spam' popup from plusnet.
I am confused.  How can an email that isn't spam suddenly become spam?

[#2]

Hi cjags,
"False positives" like that can happen. If you check the help section at webmail.plus.net you should see some information on how to report such issues.
Adam