  The fate of Cauchy horizons, such as those found inside charged black holes,
is intrinsically connected to the decay of small perturbations exterior to the
event horizon. As such, the validity of the strong cosmic censorship (SCC)
conjecture is tied to how effectively the exterior damps fluctuations. Here, we
study massless scalar fields in the exterior of Reissner--Nordstrom--de Sitter
black holes. Their decay rates are governed by quasinormal modes of the black
hole. We identify three families of modes in these spacetimes: one directly
linked to the photon sphere, well described by standard WKB-type tools; another
family whose existence and timescale is closely related to the de Sitter
horizon. Finally, a third family which dominates for near-extremally-charged
black holes and which is also present in asymptotically flat spacetimes. The
last two families of modes seem to have gone unnoticed in the literature. We
give a detailed description of linear scalar perturbations of such black holes,
and conjecture that SCC is violated in the near extremal regime.
