> I have a new server which now has SMTPUTF8 enabled. I'm not sure why
> but since then at least one Outlook client decided to stop using the
> IDN form (xn--dmin-moa0i.example) and now tries to authenticate with
> the UTF-8 domain. Researching this problem has led me to some
> questions:
When a SASL login name looks like an email address with a domain part is
an IDN (U-label) name, it seems that some clients send the login name in
A-label form when the server does not advertise UTF-8 support and
otherwise in U-label form.
This behaviour is odd, because SASL is not DNS, SASL login names are
just strings, and so the transformation is unexpected. I guess if
login names are copied into trace (Received) headers, then there is
some weak justification for making their form dependent on SMTPUTF8
support, but I rather expect that in most cases there is only one
form of the name that will match the authentication database.
So bottom line, if you have IDN domains, be aware that SASL logins
with domain parts in such domains may be affected when SMTPUTF8
support is enabled or disabled.
--
Viktor.
