Sieve matching "size" with user variable?

[Ed W]

Hi, I am trying to create a sieve filter which does something similar to 
the following:


     if size :over ${extdata.max_size} {

         # do something

     }


This doesn't seem supported in recent dovecot and size only appears to 
accept a literal number?

I'm not sure I could extra size into a variable either (to use variable 
matching). My understanding of sieve filters is that one needs to use 
something like a match, then use something like SET to put the match 
into a variable?  This syntax doesn't seem to be compatible with the 
size test here either, so I don't see that I can do this?

My goal is that users can set a user configurable setting (in an 
external front end) and if the email size is greater than this size then 
we will do some processing on it. This particular filter is actually in 
a global sieve filter.

I guess I could use an external executable program, but is there another 
way to do this?

Thanks for ideas


Ed W