Re: [Emailcore] Ticket #14: G.7.8. Review different size limits

[Viktor Dukhovni <[e-mail]>]

On Thu, Jul 15, 2021 at 12:43:07PM +0200, Alessandro Vesely wrote:

> On Wed 14/Jul/2021 23:10:22 +0200 Viktor Dukhovni wrote:
> > 
> > Logical (possibly folded across multiple physical lines) *headers* longer
> > than 100KB are truncated:
> > 
> > 	http://www.postfix.org/postconf.5.html#header_size_limit
> 
> Worded as in postconf it's not clear whether you mean a whole header rather 
> than a single header field.  In the text above, the phrase up to and including 
> the parenthesis suggests the latter interpretation.

It is *a* header field, but perhaps the text could be made more
explicit.  The text in http://www.postfix.org/header_checks.5.html
has a bit more context, but it is I guess possible to still read
it as applying to complete set of message headers as a unit.

       header_checks

       mime_header_checks (default: $header_checks)

       nested_header_checks (default: $header_checks)
              Lookup tables with  content  filter  rules  for  message  header
              lines:  respectively,  these  are applied to the initial message
              headers (not including MIME headers), to the MIME  headers  any-
              where  in  the  message,  and to the initial headers of attached
              messages.

------->      Note: these filters see one logical message header  at  a  time,
------->      even when a message header spans multiple lines. Message headers
------->      that are longer than  $header_size_limit  characters  are  trun-
------->      cated.

Anyway, bottom line, large (even unbounded) message *body* line sizes
work just fine in Postfix, but logical message headers (used in MIME
parsing, header checks, ...) do need a manageable size limit, which is
generously set at 100KiB, with longer (individual) headers truncated to
not exceed that size.

If milters are employed, then the particular milter applications would
have to deal with any larger limits, and I don't know if there's any
general statement that can be made about support for long logical or
physical message header or body lines in milters.

-- 
    Viktor.