Using Ubuntu, php 7.0.30-0ubuntu0.16.04.1, html reports says:
Sent from https://127.0.0.1/.
it only happens with scheduled reports. Download and send now doesn't have this issue. Seems that the scheduled reports follows a different code path. I've seen this since installation.
@tsteur using 3.5.1, still seeing 127.0.0.1 on scheduled emails.
I recommend to give 3.6.0 a try once released.