hey,afaik systemd timer lack the possibility to send the output (if any) by email to a designated user, but instead logs the output to its journal.
so, if you want/need that functionality, either use a wrapper script, or define a service with an 'ExecStart=' directive looking something like:
ExecStart=/bin/bash -c '/path/to/script/or/executable |& mail -E -r "<from-addr>" -s "<subject>" <user>'
(the -E flag is for /usr/bin/bsd-mailx) greetings...