3.13.0-108.155) is not available, but a newer one is (3.13.0-166.216). We redirected you there.
/usr/sbin/praliases is in sendmail-bin 8.14.4-4.1ubuntu1.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/sbin/../lib/sm.bin/praliases