(Adding to this thread because we only just now hit this issue …)
> On Nov 18, 2021, at 15:00, Jeremy Harris via Exim-users <exim-users@???> wrote:
>
> On 18/11/2021 10:35, Andrea Biscuola via Exim-users wrote:
>> One week ago, we upgraded to exim 4.95 and suddenly, some customers (using microsoft
>> outlook, nonetheless), started to experience the following error for *some* of their
>> e-mails:
>> message has lines too long for transport
>> Reporting-MTA: dns; web017.shared.host.it
>> I received some examples of such e-mails from our customers service, and it appear that
>> the problem is with some badly formatted headers.
>> Unfortunately, we can't throw those customers out of the window :-) so we are searching
>> how to expand the line limits for the transports.
>
> Warning: you would be sending onward messages that are explicitly
> exceeding the limits established by the relevant standards.
>
> Any such might be lost (or worse, cause "unintended actions") on
> other systems they traverse after yours.
>
> Are you certain you want to be responsible for that?
> You might wish to consult your legal staff.
RFC 5322 doesn’t stipulate server behaviour upon receipt of a message that violates this limitation.
On the contrary, the same section (2.1.1) that gives the 998-character limit adds, in the next paragraph:
----
Receiving implementations would do well to handle an arbitrarily large number of characters in a line for robustness sake.
----
While Exim’s new default behaviour is reasonable, it doesn’t seem to follow from the relevant standard. Outlook is in violation, to be sure, but servers that accept arbitrarily long lines don’t seem to be (by that virtue alone, anyhow).
-FG
