  In this paper, recent abstract multiplier theorems for $0$-sectorial and
$0$-strip type operators by Kriegler and Weis (2018) are refined and
generalized to arbitrary sectorial and strip-type operators. To this end,
holomorphic H\"ormander-type functions on sectors and strips are introduced
with a scale of smoothness being finer than the classical polynomial one.
Moreover, we establish alternative descriptions of these spaces involving
Schwartz and "holomorphic Schwartz" functions. Finally, the abstract results
are combined with a recent result by Carbonaro and Dragi\v{c}evi\'c (2017) to
obtain an improvement -- with respect to the smoothness condition -- of the
known H\"ormander-type multiplier theorem for general symmetric contraction
semigroups.
