dovecot - Dec 2013 - configure lmtp to deliver to email addresses case insensitively

Dear List

Using dovecot 2.1.7 with LMTP and exim4 I want to accept local parts 
regardless of their case.

Exim does all virtual alias handling and delivers the messages to 
dovecot LMTP addressed to the right mailbox name. This works well except 
for addresses which do not need to be resolved by exim and which do have 
the "wrong" case in the local part.

For example: There is a mailbox and a user on the mailsystem 
"example.org" called "user". Mails to "user at
example.org" get delivered
just as they should. If an incoming message is addressed to 
"USER at example.org" with upper case local part, exim passes the
message
to LMTP with the case unaltered (RFC 2821 conform), but LMTP fails with:
     LMTP error after RCPT TO:<USER at example.org>:
     550 5.1.1 <USER at example.org> User doesn't exist:
     USER at example.org

How can I tell dovecot to deliver "USER" to the mailbox
"user" aswell?

Thank you for your help.

Best regards, Adrian.

(I have tried to use %Ln and %Lu in mail_location setting with no success.)

On 2013-12-16 2:36 PM, Adrian Zaugg <adi at ente.limmat.ch>
wrote:
> How can I tell dovecot to deliver "USER" to the mailbox
"user" aswell?
"Username

LDAP lookups are case-insensitive. Unless you somehow normalize the 
username, it's possible that a user logging in as "user",
"User" and
"uSer" are treated differently. The easiest way to handle this is to 
tell Dovecot to change the username to the same case as it's in the LDAP 
database. You can do this by returning "user" field in the pass_attrs,
as shown in the above example.

If you can't normalize the username in LDAP, you can alternatively 
lowercase the username in dovecot.conf:

auth_username_format = %Lu"

See: http://wiki2.dovecot.org/AuthDatabase/LDAP/PasswordLookups

This really should be the default...


-- 

Best regards,

*/Charles/*

Hi David
> I believe RFC822 email addresses are case-insensitive, and (in some
RFC 2821, Page 13, 1st paragraph:
   "The local-part of a mailbox
   MUST BE treated as case sensitive.  Therefore, SMTP implementations
   MUST take care to preserve the case of mailbox local-parts.  Mailbox
   domains are not case sensitive.  In particular, for some hosts the
   user "smith" is different from the user "Smith". 
However, exploiting
   the case sensitivity of mailbox local-parts impedes interoperability
   and is discouraged."
(http://tools.ietf.org/html/rfc2821#section-2.4)
> cases, especially ones where there's just a mail server) it's
entirely
> possible that people remember their account names  with some capital
> letters that aren't in user db. (System knows you as
> "mrsmithy at mail.domain", while the user may remember the
account as
> "MrSmithy at mail.domain" or "MrsMithy at
mail.domain"...). Also, people with
I just want login names to be case sensitive but not email addresses,
and in spite of being treated as case insensitive email addresses should
retain their case, just like defined and suggested in the RFC.

This reduces support calls because it's con-formant and we have a clear
policy: Usernames are always lower case, non-email addresses, the same
simple and short name for all our services. There is nothing easier than
this. We use this since 17 years and it works without confusion. If a
user now spots that suddendly any capitalization of usernames is working
when logging in to the webmail, how can I explain that this doesn't work
with other services like FTP?
> smartphones may not notice that the phone "helpfully" uppercased
the
> first letter of a lowercase user name. Forcing case reduces support
> calls, which is always a good thing.
That's why email addresses should be allowed containing capitalizations.
On smartphone people tend to use MUAs and there the username is saved
and not entered each and every time, so for the username this is less
true, I think.

Back to dovecot: Using LDA as a transport for the dovecot store, it used
to work perfectly (with dovecot 1.x). It's just LMTP that spits, because
it looks up the local part in the userdb, which is PAM in our case. I
won't change PAM to act case insensitive: I'm not in the position to
change a common sense in the computing world as it always was. It's
enough Microsoft did that and probably just because of that we're having
this discussion here...

However, it's maybe best to lowercase the local part in the exim
lmtp-transport and leave dovecot's LMTP in peace.

Best regards, Adrian.