Who builds the email header when using sieve

[Daniel Stellwagen]

Hi everybody,

can someone tell me which part of cyrus is building the email header 
when sending a respond message back to a sender like this:

# Mail rules for user daniel
# Created by easysieve version 1.2
require ["vacation","reject"];

vacation :days 3 :addresses "Daniel.Stellwagen at brunata-muenchen.de" text:
Hi, I am on vacation.
.
;

I ask because I want to change the "Content-Type:" content.


Thanks

d a n i e l
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