[exim] What does exim do with malformed messages?

If a malformed mail message shows up by SMTP (not local sendmail or submission),
will exim generally try to clean it up or just pass it along?

I see the discussion of submission mode in chapter 48 of the manual and all the
options about when to run it and what to tell it to do, but in practice, will a
typical system clean everything up, just locally submitted stuff, or soemthing
else? Tnx.

I'm thinking of stuff like this that might come from a badly written gateway:

From: fred at example.com
Message-Id: something@somethingelse
Date: Tuesday, 28 Nov 2023 18:17:05 GMT

R's,
John

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