The act of putting letters, postcards, or envelopes into a mailbox or postbox for mailing. Used as a noun and in the verb form (to post/mail).
郵便受けに広告を投函しないでください。
Please do not put advertisements into the mailbox.
明日、書類を郵便局のポストに投函します。
I'll post the documents in the post office box tomorrow.
投函前に宛先と切手が正しいか確認してください。
Please check that the recipient address and stamp are correct before posting.