Correct spelling for the English word "posthastle" is [pˈə͡ʊsthe͡ɪsə͡l], [pˈəʊstheɪsəl], [p_ˈəʊ_s_t_h_eɪ_s_əl] (IPA phonetic alphabet).
With speed.
Etymological and pronouncing dictionary of the English language. By Stormonth, James, Phelp, P. H. Published 1874.