You may configure the service to start after connecting to the network and mounting a fileshare if you wish. Find the name of the fileshare:
systemctl list-units --type=mount
and you should see something like mnt-foobar.mount. Add that to your service:
[Unit]
Description=Automatic backup service
After=network.target mnt-foobar.mount
OnFailure=notify-email@%i.service
For me, this was causing failures because it wasn't waiting for that mount. I had a VPN configured to autoconnect on login with another service, and it blocked my backup because it couldn't access my cifs volume. Now to hunt it down and make it load only after my backup service has run.