Outlook Express is a

Concept

Internet application software is classified by the network task it performs. An e-mail client is a desktop program used to send, receive, store, and organise electronic mail by connecting to mail servers over protocols such as POP3, IMAP, and SMTP. A web browser, by contrast, renders web pages, and a search engine is a web service that indexes pages and returns results for a query.

Application

Outlook Express is the e-mail and newsgroup program that Microsoft bundled with Internet Explorer and Windows (98 through XP). Its core job is managing mail accounts and messages through POP3/IMAP/SMTP, which is exactly the definition of an e-mail client.

Contrast

• Browser: software for viewing web pages (Internet Explorer, Chrome) — Outlook Express does not render web pages as its purpose, so this does not fit.

• Search engine: an online query-and-index service (Google, Bing) — it is a website, not a desktop mail program, so this does not fit.

• None of the above: an exact category does fit, so this catch-all is unnecessary.

Therefore Outlook Express is best described as an e-mail client.