Email client
The program or app a person uses to read and write email, such as Outlook, Apple Mail, Thunderbird or the Gmail app; in standards terms, a Mail User Agent.
What it means
An email client is the MUA of RFC 5598: it fetches mail from the mailbox (over IMAP, POP or a provider's own interface), displays it, and sends new messages through a submission server. Some run on a desktop or phone, others in a browser as webmail, and many people read one mailbox in several.
Clients matter to senders because each renders HTML and CSS its own way, decides whether to load images, builds its own preview text and decides whether to show an unsubscribe button. Can I email tracks feature support across clients, and testing in the clients a list actually uses is the reliable way to know how a message will look.
Related terms
On this site
Sources
What this definition rests on. The wording is ours; the facts are theirs.
- RFC 5598, section 4.2.1: Message User Agent (MUA)rfc-editor.org
- Can I email: HTML and CSS support across email clientscaniemail.com
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