• 郵便ゆうびん — mail; postal service
• 郵送ゆうそう — mailing; sending by post
• 郵便局ゆうびんきょく — post office
• 郵袋ゆうたい — mailbag

郵 originally referred to relay stations along roads in ancient China, where officials or messengers would change horses. From this idea of communication posts, the character came to mean “mail” or “postal system.”

郵便ゆうびんで 手紙てがみを 送おくりました。
I sent a letter by mail.

郵便局ゆうびんきょくは この近ちかくにありますか？
Is there a post office nearby?