。
I just got back from the post office.
Literal
Post-office [to-へ] go-[come-back-てきた]-just-[place-ところだ].
~たところだ is the 'just now' aspectual marker, distinguishable from the resultative ~ている and the lexical すぐ. It specifies that the action was completed moments ago. 行ってきた stacks 行く + てくる ('go and come back'), so 行ってきたところだ is literally 'just finished going-and-coming-back.' A tidy aspectual chain.