[Exim] Text for :fail:

exim4, section 21.6 says the text following :fail: when verifying an address for
SMTP RCPT is used in the 550 response. I have an ACL with no "message" statement
which causes recipient verification and a router which generates

:fail: Unroutable domain "loc-part@dom-part"

I find that a -bh test ends with

550 Unknown user "loc-part" at "dom-part"
LOG H=... rejected RCPT <loc-part@dom-part>: Unroutable domain "loc-part@dom-part"

Is this a bug or a documentation error? If the latter, then it seems odd to allow
and text after the :fail:.

Phil.
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Phil Chambers (postmaster@???)
University of Exeter