From Longman Business Dictionary
mailshotmail·shot /ˈmeɪlʃɒt-ʃɑːt/ noun [countableC] British EnglishBrEMARKETING when information or advertising material is sent through the mail to a large number of people at one time, or the information or advertising material sent in this waySYN MAILINGI received a mailshot telling me I had won a free holiday.