Reply-To header
The header field giving the address replies should go to when that is not the From address; mail programs use it when the reader clicks Reply.
What it means
RFC 5322 makes Reply-To optional. When present it holds one or more addresses the author suggests for replies; when absent, replies go to From. Typical uses are a no-reply From with replies routed to a support desk, a newsletter whose replies go to a named person, or a mailing list directing discussion back to the list.
Nothing checks that the Reply-To address belongs to the sender: SPF and DMARC authenticate other identities. A convincing From with a Reply-To at another domain is therefore a common pattern in fraud, and worth checking in any message that asks for money or credentials. Google's guidelines list the reply-to domain among the domains that must follow its formatting rules for internationalized domain names.
Related terms
Sources
What this definition rests on. The wording is ours; the facts are theirs.
- RFC 5322, section 3.6.2: Originator Fieldsrfc-editor.org
- Google, Gmail Help: Email sender guidelinessupport.google.com
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