Should I use the Reply-To header when sending emails as a service to others?

Suppose we have an application that acts as a middleman, allowing Company A to send reports to their customers.

> Company A --> Company B (me)--> Company A's customers

After getting the report we send email notifications to the recipients, but they necessarily originate from our company notifications email address e.g.

> [email protected] --> [email protected] --> [email protected]

Now, customers tend to reply to those email notifications, wanting them to go back to whoever sent the report at Company A. Instead, they end up back at our address, [email protected].

A simple solution may be to change the Reply-To header on the notifications we send to the relevant Company A address e.g.

> [email protected] --> [email protected] [Reply-To: [email protected]] --> [email protected]

But my main concerns are:

• the complete discrepancy in email address and domain between the From and Reply-To fields might make spam or phishing filters more eager to flag the emails
• not all email clients may respect the Reply-To field when people actually click "Reply", and just use From instead. A lesser concern, unless widespread.

Are these concerns founded at all? Or, are there other concerns I should have?

I tested dkarp's solution with gmail and it was filtered to spam. Use the Reply-To header instead (or in addition, although gmail apparently doesn't need it). Here's how linkedin does it:

Sender: messages-noreply@bounce.linkedin.com
From: John Doe via LinkedIn <member@linkedin.com>
Reply-To: John Doe <John.Doe@gmail.com>
To: My Name <My.Name@gmail.com>

Once I switched to this format, gmail is no longer filtering my messages as spam.

You may want to consider placing the customer's name in the From header and your address in the Sender header:

From: Company A <joe.bloggs@a.com>
Sender: notifications@b.com

Most mailers will render this as "From [email protected] on behalf of Company A", which is accurate. And then a Reply-To of Company A's address won't seem out of sorts.

From RFC 5322:

> The "From:" field specifies the author(s) of the message, > that is, the mailbox(es) of the person(s) or system(s) responsible > for the writing of the message. The "Sender:" field specifies the > mailbox of the agent responsible for the actual transmission of the > message. For example, if a secretary were to send a message for > another person, the mailbox of the secretary would appear in the > "Sender:" field and the mailbox of the actual author would appear in > the "From:" field.

After reading all of this, I might just embed a hyperlink in the email body like this:

To reply to this email, click here <a href="mailto:...">[email protected]</a>

I was looking into this recently, my answer is same as others, however, I believe its definitions are clearer to a layman:

1. From should be described as the author of the message
2. Sender should be described as the transmitter of the message
3. Reply-To should not be confused with 1 and 2, it simply means where the receipient should write to if they choose to respond

Thus in some clients (e.g. Outlook 2003), you will see

> From: Sender on behalf of From

Here is worked for me:

Subject: SomeSubject
From:Company B (me)
Reply-to:Company A
To:Company A's customers