Re: [exim] Message rejected due to long Reference: header

On 16/04/2019 10:18, Graeme Fowler via Exim-users wrote:
> On 16 Apr 2019, at 04:27, Konstantin Boyandin (lists) via Exim-users <exim-users@???> wrote:
>> Is there any Exim setting capable of re-formatting long headers (i.e., split them into several lines, each below 998 character limit) etc such headers, but allowing the incoming mail nonetheless?
>
> I feel your pain; I had to migrate 20000 or so student mailboxes from Gmail to Exchange Online (Office 365) a couple of years back and there were thousands of messages with over-long lines (but not headers!) and EOL would not accept them. We used imapsync which allows in-flight modification of the message, so we split at 998 chars and added \r\n as a line break. Anyhow...

The 998 limit is for de-folded lines. Go over that and you'd need
multiple header lines; to do which you'd have to be duplicating
header_names: as well as adding linebreaks. And yes, that would
very likely break DKIM signatures.

The folding limit is 78.

No, there's no builtin in Exim to do that. You could program
it in ACL, but it's some fair amount of work - especially if
you want to try to identify "high level semantic break points"
as suggested by RFC for line-folding.
--
Cheers,
Jeremy