Thanks for the reply caisson. 

No it's a POP server.  Most email gets classified correctly and Pegasus hadn't been touched for about a year. The problem has only been noticed in the last few weeks.

I have updated to 4.7  but the behaviour is the same.

Spanhalter has been (still is as this is just an irritation) amazing for me - accurate and easy to use. 

Some emails arrive with the spam traffic lights both greyed out and

the message "This message has no or uncertain spam classification"  appers in the hover over box.   They are not all

spam.  When the spamhalter clasification is explained:

• they all say that the "stored spam probablity" is zero
• "Current spam probability" gives an appropriate classification (typically 0 if not spam 100 if spam

Is this with an IMAP account.  There has been been previous discussion along these lines involving IMAP accounts.

I've never used Spamhalter, preferring POPFile, but my recollection is that Spamhalter doesn't work with IMAP.