off
1.
to shoot a bullet from a gun :
They fired off a volley of shots.
2.
to write or say sth to sb very quickly, often when you are angry :
He fired off a letter of complaint.
She spent an hour firing off emails to all concerned.
FIRE STH
Meaning of FIRE STH in English
Oxford Advanced Learner's English Dictionary. Оксфордский английский словарь для изучающик язык на продвинутом уровне. 2005