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

Question

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: [email protected]
From: John Doe via LinkedIn <[email protected]>
Reply-To: John Doe <[email protected]>
To: My Name <[email protected]>

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 <[email protected]>
Sender: [email protected]

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>