[Dovecot] Is there a hook for a plugin to do some transient operation on the mail body ...

[Jay]

... when the MUA has issued a FETCH?
 
I am a Dovecot newbie ... so please bear with me if this is obvious. Basically what I am trying to do is process the mail body (in my own specific way) before Dovecot serves it up to the MUA. I want to do it as a transient operation in memory. So think of the scenario as ...
  - the MUA issues a FETCH
  - Dovecot intercepts the FETCH
  - Dovecot internally gets the mail from the storage into a buffer in memory
  ----> This is where I'd like to apply a function to the mail body and modify the mail body in the buffer (not in the storage)
  - Dovecot serves up the (modified) mail to the MUA
 
Looking for a hook that allows me to do it using a plugin. Looks like the zlib plugin does something similar ... applies a decompression function ... but I am not 100% sure.
 
Thanks for your help.
-- J.