On Wed, 24 Feb 1999, Bruce Bowler wrote:
> 1) Check as now, if found - deliver
> 2) Check as presented in address, if found - deliver
Remember that "deliver" in Exim terms means "send to a specific
transport". The transport, however, may itself want to use the local
part in some way - e.g. in /var/mail/$local_part - and so it too needs
to know what case to use.
I had the following thoughts overnight:
1. Unix user names are caseful.
2. People out in the world expect email local parts to be
case-independent.
3. We can probably assume that no Unix system admin will create two
accounts that differ only in their case.
4. Therefore, the problem is to find the correctly cased version of an
incoming local part.
5. Exim's default algorithm for doing this is "lower case it", because
that works in by far the majority of cases. (I would suspect it
really is around 99%.)
6. Exim's alternative algorithm is "leave it alone".
7. I cannot see that there are any other "obvious" algorithms that it
would be sensible to build in.
8. So, we have to find some way for the admin of such a system to
provide one.
9. It's not just a matter of persuading the localuser director to use
the right value - it has got to be available in other places as well,
e.g. for .forward files and for the mailbox name.
10. Therefore, the tidy way to do it is to transform the local part at
the start of processing, so that everything else uses the correctly
cased local part.
11. The smartuser director can be used to do this. If locally_caseless
is set false, and the first director
is
fix_case:
driver = smartuser
new_address = <some magic>@$domain
then it will create a modified new address that is handled by
everything else. (For maximum efficiency, it would be best to set
new_director = name_of_subsequent_director
to save it reprocessing the new local part again. The problem now
reduces to finding what to use for <some magic>.
12. If you have a simple algorithm, e.g. "first two characters are
always upper case, rest is lower case" you can write a string
expansion that does it:
new_address = "${uc:${substr_0,2:$local_part}}\
${lc:${substr_2:$local_part}}@$domain"
which might work for BBowler, but probably not for root. If you want
to do something esoteric such as read /etc/passwd and do caseless
matching, or fuzzy matching, or anything else, you can use the
embedded Perl feature of Exim to get it to run a Perl function for
you:
new_address = ${perl{$fix_local_part}{$local_part}}
That is expensive, of course, but it will allow you to implement any
rule you choose.
--
Philip Hazel University of Cambridge Computing Service,
ph10@??? Cambridge, England. Phone: +44 1223 334714.
--
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