Mail has stopped saving my previous recipients
Mac Pro 10.6.8
Mail 4.6 (1085)
Mail has always saved any e-mail addresses I have sent to in the past which is a handy feature, about 6 months ago it stopped, I thought the previous recipients might be full so I deleted some but it did nothing.
I have searched but can only find people trying to delete previous recipients and not the other way around.
I don't want to have to add each person to my address book (as I know it is unnecessary as it worked without doing this for years)
Thanks for any help in advance.