[Exim] square brackets in To header

Hello All!

I have Exim server running in production environment for 6 months
and had no problem with it.
But now this thing is driving our customers mad.
The case is that someone is trying to sent messages with receiver
in form Customer Name [some info] <email@domain>
I've checked this form of address with -bt option and Exim reports it
as "missing or malformed local part".

Any help appreciated.

-- Alexei