邮件是指经传递方式处理的文档。邮件传递的过程称为「邮递」，而从事邮递服务的机构或系统，则称为邮政。

常见的邮件种类包括书信、邮简、明信片、单据（如月结单、电费单、水费单等）等文档类物品，以及体积较大的包裹，广义上可再加上新闻纸、杂志、印刷品、盲人文档。基本上，只要符合邮政要求的格式，任何文档皆可成为一个邮件。而电信技术在19世纪开始发展后，邮件的概念亦扩展至电子通信领域，如电报、传真、电子邮件、手机短信等。

由于邮政系统具有维持为公众传递消息的重要功能，通常被视为公用事业的一环，也因此世界各地的邮政系统大多为公营事业。各邮政系统基本上均有快递业务，由于快递与物流的性质类似，部分较具规模的邮政机构甚至会跨足经营物流事业。

The mail or post is a system for physically transporting documents and other small packages, as well as a term for the postcards, letters, and parcels themselves. A postal service can be private or public, though many governments place restrictions on private systems. Since the mid-19th century national postal systems have generally been established as government monopolies with a fee on the article prepaid. Proof of payment is often in the form of adhesive postage stamps, but postage meters are also used for bulk mailing. Modern private postal systems are typically distinguished from national postal agencies by the names "courier" or "delivery service".