邮政局是邮政系统中的基本设施。

它负责邮件的投寄、收件、分类、处理、发送及交付。邮政局亦会提供其他邮政相关的服务，例如邮政信箱、邮资及包装供应。另外，一些邮政局亦会提供非邮政服务，如处理护照及其他政府表格的申请、汇票，以及银行、保险等金融服务。

对于不想在家中或办公室收件的人，或居住地点偏僻而无法使用邮政服务的人，邮政局会对他们借出邮政信箱（设于邮政局内），令他们可在邮政局中收件。

邮政局的内房会用作处理邮件的分类及交付。邮件亦会被一些不对公众公开的邮政局（没有服务柜台的邮件处理中心）去处理。

A post office is a customer service facility forming part of a national postal system. Post offices offer mail-related services such as acceptance of letters and parcels; provision of post office boxes; and sale of postage stamps, packaging, and stationery. In addition, many post offices offer additional services: providing and accepting government forms (such as passport applications), processing government services and fees (such as road tax), and banking services (such as savings accounts and money orders). The chief administrator of a post office is a postmaster.