Reply-To is not the From mailbox

Reply-To names a reply destination

Reply-To, when present, is the mailbox a client may use if someone presses reply. It is a header on the message. It is not an authentication result, and it is not the display name.

This page does not send a reply. Recording the header is the whole task.

From names the header mailbox

The mailbox on the From line is the sender address in that header. It can differ from Reply-To. A draft that swaps them will name the wrong mailbox as the sender and the wrong mailbox as the reply destination.

If Reply-To is absent, a client usually replies to From. Write that Reply-To is not in this copy. Do not copy From into a Reply-To field you invented.

Lines that stay apart

File the From mailbox and the Reply-To mailbox with those labels. Add the display name only if you are also discussing that label, and keep it off both address lines.

Lab: a reply address on another domain

A lab message has From notices@lab-mail.example and Reply-To desk@other.example. A draft says the sender is desk@other.example because that is where a reply would go.

The note lists notices@lab-mail.example as From and desk@other.example as Reply-To. The reply destination is not renamed into the sender. No reply is sent.

Snippet

From: notices@lab-mail.example
Reply-To: desk@other.example
write: sender mailbox and reply destination
not: sender desk@other.example

Diagram

Keep the sender mailbox off the reply destination

From
The mailbox on the From line.
Header
```
notices@lab-mail.example
```
Reply-To
Where a client may send a reply.
Header
```
desk@other.example
```
A reply
Not sent from this page.
Note
```
record only
```
Absent Reply-To
Say the header is not in the copy.
Note
```
do not invent it from From
```

Check yourself

1. From is notices@lab-mail.example and Reply-To is desk@other.example. Which mailbox is the sender on the From line?

2. Where may a client send a reply when Reply-To is present?

3. Reply-To is absent. What do you write?