Potential issues using member's “from” address and the “sender” header

Question

A major component of our application sends email to members on behalf of other members. Currently we set the \"From\" address to our system address and use a \"Reply-to\" he

Answer 1

So I decided to answer my own question since no one else responded. Perhaps others will find this entry when searching.

What we're finally doing is this:

Set the From header to the user's actual email address.

From: "Mary Smith" <marysmith@memberisp.example>

Use a Sender header with the system wide email address.

Sender: <messages@company.example>

Finally, the actual sender that shows up in the server supplied MAIL FROM/Return Path header is set with a unique identifier, i.e.,

Return Path: "Mary Smith" <messages+ca54bb7482ace09f@company.example>

That allows a program running at messages@company.example to intercept those auto replies and forward them onto the person they were originally intended to reach. Most real email clients will reply to the From: header. I haven't seen problems from blackberry users nor others responding to the system account.

After a month or so in production, we've had fewer issues with this than the previous method we were using.

The Sender header adds a small note in Microsoft Outlook clients about "On Behalf Of" but that's appropriate for our usage. There haven't been any issues with SPF in common clients/mta with this setup (Gmail, Yahoo, SpamAssassin, etc.)

Update: In April 2014, Yahoo and AOL changed their DMARC settings to drop these kinds of messages without notice. (They switched to p=reject; see https://wordtothewise.com/2014/04/brief-dmarc-primer/ for more information.) Our solution was to special case those domains, since the needed functionality still works with the vast majority of domains.

IF ISP MATCHES YAHOO OR AOL

From: "Mary Smith" <messages+ca54bb7482ace09f@company.example>
Reply-To: "Mary Smith" <marysmith@memberisp.example>
Return Path: "Mary Smith" <messages+ca54bb7482ace09f@company.example>

ELSE

From: "Mary Smith" <marysmith@memberisp.example>
Sender: <messages@company.example>
Return Path: "Mary Smith" <messages+ca54bb7482ace09f@company.example>

END