[Exim] Bug: Automatic re-routing of domains

Hello!

(I have replaced all @s with # below, to protect email addresses)
When doing an address verification test for abuse#dot.tk, I get the
following debug log from Exim 4.20:

>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
Testing abuse#dot.tk
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
Considering abuse#dot.tk
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
routing abuse#dot.tk
[...]
--------> dnslookup router <--------
local_part=abuse domain=dot.tk
checking domains
dot.tk in "muelli.net"? no (end of list)
dot.tk in "! +local_domains"? yes (end of list)
calling dnslookup router
dnslookup router called for abuse#dot.tk
domain = dot.tk
DNS lookup of dot.tk (MX) succeeded
DNS lookup of ATAFU.TALOHA.TK (AAAA) gave NO_DATA
returning DNS_NODATA
DNS lookup of ATAFU.TALOHA.TK (A) succeeded
195.20.32.97 in "0.0.0.0 : 127.0.0.0/8"? no (end of list)
fully qualified name = DOT.TK
host_find_bydns yield = HOST_FOUND (2); returned hosts:
ATAFU.TALOHA.TK 195.20.32.97 0
domain changed to DOT.TK
rewriting header lines
re-routed to abuse#DOT.TK
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
Considering abuse#DOT.TK
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
routing abuse#DOT.TK
[...]
--------> dnslookup router <--------
dnslookup router skipped: previously routed abuse#dot.tk
--------> system_aliases router <--------
[...]
======================================================================

Obviously, the dnslookup router first changes the domain from dot.tk
to DOT.TK, and subsequently skips the address, because it thinks it
has already routed it. The address is then processed by the local
routers and finally delivered to abuse@local_domain.

Proposed solution: Exim should ignore differences in the case of
letters when doing automatic domain re-routing. After all, domains
are routed case-insensitively.

Andy