[exim/exim] [RFE] Change default encoding from us-ascii to utf-8 (Issue #3198)

---------------
Feature Summary
---------------

I would like the messages sent by deliver.c to default to utf-8 instead of us-ascii.

-----------------
Problem Statement
-----------------

Allow e.g. subject to contain unicode chars.

-----------------
Proposed Solution
-----------------

Replace all occurences us-ascii with UTF-8

-----------------------
Alternatives Considered
-----------------------

Adding

Content-Type: text/plain; charset=UTF-8
Subject: Warnung/Warning: $rh_subject

to warn_message_file causes errors in rspamd (MULTIPLE_UNIQUE_HEADERS).

---
View it on Exim Forgejo ( https://code.exim.org/exim/exim/issues/3198 ) or reply to this email directly.