mail attribute has the following syntax.
IA5String (OID=18.104.22.168.4.1.1422.214.171.124.26) IA5 (almost ASCII) (...)
This is why you cannot give non-ascii characters.
Yes. It's an attribute standardized with that definition (derived from
RFC 1274), and OpenLDAP follows the standard.
It is a bug.
A design bug, perhaps, but not an OpenLDAP bug. This ITS will be closed.
These attributes were designed quite a while ago by Europeans and
Americans who clearly didn't pay too much attention to the rest of the
world, but then it was before the age of computer internationalization.
About 'mail', I'm not sure what sense 8-bit values would make since
since SMTP could rewrite it to 7-bit. I could not send e-mail to an
8-bit address, but maybe it works where you live. OTOH, there is some
standard for how to represent 8-bit domain names in ASCII. Maybe there
is for 8-bit addresses too.
telephoneNumber and facsimileTelephoneNumber are supposed to contain
numbers in a 7-bit international format, E.123. It's irritating that
one cannot include 8-bit comments along with such a number, but that's
the standardized definition.
Another and more irritating 7-bit attribute is 'gecos' from RFC 2307
(nis.schema in OpenLDAP). There is a draft revision of this one
("rfc2307bis") which I think revises it to 8-bit, but I don't know the
status of that draft.