  In this letter, we show that in the usual type-I seesaw framework, augmented
solely by a neutrino portal interaction, the dark matter (DM) relic density can
be created through freeze-in in a manner fully determined by the seesaw
interactions and the DM particle mass. This simple freeze-in scenario, where
dark matter is not a seesaw state, proceeds through slow, seesaw-induced decays
of Higgs, $W$ and $Z$ bosons. We identify two scenarios, one of which predicts
the existence of an observable neutrino line.
