[Dovecot] antispam plugin claims "antispam signature not found"

[Jakob Curdes]

> plugins {
>   antispam_trash = trash;Trash;Deleted Items
>   antispam_spam = SPAM;Spam;Junk
>   antispam_dspam_args = --client;--deliver=;--user;%u
>   
I am using dspam in a different setup; I run it under amavis so the user 
is always the user amavis. I don't run a daemon so --client makes no 
sense. What does "deliver=" do? Is that the same as 
"deliver=innocent,spam" ?

I think it must be related to permissions in some way but I do not see 
how. I would like to debug it further but am no C programmer. I cannot 
see why it is not able to extract the signature.

JC