From Longman Dictionary of Contemporary Englishby return (of post)by return (of post)British EnglishTCM if you reply to a letter by return, you send your reply almost immediately → return
Examples from the Corpus
by return (of post)• Please answer by return of mail.• Any sent will be copied and sent back by return of post.• Professor Sano writes back by return mail.• Companies are classified by returns, and all companies with an equivalent return have the same business risk.• I end it by returning to those encounters.• Earlier this year, the Dole campaign alienated many Log Cabin members by returning a campaign contribution from the gay organization.• But Smith bailed them out by returning seven punts for a school-record 150 yards.• He was given 25 years but tried to negotiate a cut in his sentence by returning half of the stolen gold. 