On 20 Dec 2019, at 18:08, Jack Bailey via Exim-users <exim-users@???> wrote:
> header_maxsize was not in my exim.conf. It is now.
Something is definitely wrong here - if that is unset in your config, it should be 1M by default (set in Local/Makefile at build time). From the docs:
> header_maxsize Use: main Type: integer Default: see below
> This option controls the overall maximum size of a message’s header section. The default is the value of HEADER_MAXSIZE in Local/Makefile; the default for that is 1M. Messages with larger header sections are rejected.
I would be very, very surprised if whatever OS your package has come from has overridden that with an insanely large number.
You don’t have any header rewrite rules, filter rules or something like procmail/formail/sieve doing anything weird, do you?