USE="exiscan" is of no use in exim-4.62.ebuild, because the only file it should install isn't there anymore.
the file was moved onto the mirrors as per bug #100369 and partially #120459, I'll take a look this evening as to what the issue is.
$ ebuild exim-4.63.ebuild fetch >>> Downloading 'ftp://ftp.sh.cvut.cz/MIRRORS/gentoo/distfiles/exim-4.63.tar.bz2' --18:36:18-- ftp://ftp.sh.cvut.cz/MIRRORS/gentoo/distfiles/exim-4.63.tar.bz2 => `/usr/portage/distfiles/exim-4.63.tar.bz2' Resolving ftp.sh.cvut.cz... 147.32.127.222 Connecting to ftp.sh.cvut.cz|147.32.127.222|:21... connected. Logging in as anonymous ... Logged in! ==> SYST ... done. ==> PWD ... done. ==> TYPE I ... done. ==> CWD /MIRRORS/gentoo/distfiles ... done. ==> PASV ... done. ==> RETR exim-4.63.tar.bz2 ... done. Length: 1,586,169 (1.5M) (unauthoritative) 100%[===================================================================================================>] 1,586,169 181.31K/s ETA 00:00 18:36:28 (204.23 KB/s) - `/usr/portage/distfiles/exim-4.63.tar.bz2' saved [1586169] >>> Downloading 'ftp://ftp.sh.cvut.cz/MIRRORS/gentoo/distfiles/exiscan.conf' --18:36:28-- ftp://ftp.sh.cvut.cz/MIRRORS/gentoo/distfiles/exiscan.conf => `/usr/portage/distfiles/exiscan.conf' Resolving ftp.sh.cvut.cz... 147.32.127.222 Connecting to ftp.sh.cvut.cz|147.32.127.222|:21... connected. Logging in as anonymous ... Logged in! ==> SYST ... done. ==> PWD ... done. ==> TYPE I ... done. ==> CWD /MIRRORS/gentoo/distfiles ... done. ==> PASV ... done. ==> RETR exiscan.conf ... done. Length: 22,113 (22K) (unauthoritative) 100%[===================================================================================================>] 22,113 65.66K/s 18:36:29 (65.56 KB/s) - `/usr/portage/distfiles/exiscan.conf' saved [22113] * checking ebuild checksums ;-) ... [ ok ] * checking auxfile checksums ;-) ... [ ok ] * checking miscfile checksums ;-) ... [ ok ] * checking exim-4.63.tar.bz2 ;-) ... [ ok ] * checking exiscan.conf ;-) ... [ ok ] Closing a stale bug.