MAIL FROM command
The SMTP command that opens a mail transaction and gives the envelope sender, the address that bounces and delivery reports are sent back to.
What it means
The syntax is MAIL FROM:<address>, optionally followed by extension parameters such as SIZE=, BODY=8BITMIME, RET= and ENVID= for delivery status notifications, or SMTPUTF8. The address in the brackets becomes the envelope sender. It can differ from the From header the reader sees, and for mail sent through a platform it usually does, pointing at an address where the platform processes bounces. The empty form, MAIL FROM:<>, is the null sender reserved for bounces and other notifications.
The receiving server can refuse the sender at this point, before any recipient is named, for example when the sender domain publishes a null MX (550 5.7.27). SPF checks the domain of this address, which is why the domain used here matters for authentication and, through alignment, for DMARC.
Example
MAIL FROM:<bounces+7f3a@mail.example.com> SIZE=48213 BODY=8BITMIMERelated terms
On this site
Sources
What this definition rests on. The wording is ours; the facts are theirs.
- RFC 5321, section 4.1.1.2: MAIL (MAIL)rfc-editor.org
- RFC 7208, section 2.4: The "MAIL FROM" Identityrfc-editor.org
- RFC 7505, section 4.2: Sending Mail from Domains That Publish Null MXrfc-editor.org
All 432 terms in the glossaryThe wiki: blocklists and bounce codes