Best practices: Sending email on behalf of users
The company I work for provides testing services for the healthcare industry. As part of our services, we need to send email to our clients' employees. Typically, these are temp, part-time, or contract employees, and so have private email addresses (eg Hotmail, GMail, Yahoo!, etc).
Up to now, we've been sending from an internal address, but this means that replies come back to us when employees aren't paying attention or don't know to send queries to our clients. I'd like to change this, so that the person who requests that the email is sent is the person that is replied to.
We've used reply-to: in the past, but it seemed to cause additional mail to be trapped by spam filters.
I've been reading about sender: and on-behalf-of: headers, and was wondering what the current best-practice was for sending email in a scenario where we need to send email such that the reply goes to a domain we don't control.
Answer
The on-behalf-of header is the best way to do that, but you are also going to get trapped by spam filters. The best to mitigate or lessen the likelihood that you will end up in the spam filter is to implement all the industry standards around verifying your domain and mail server. As indicated in this article:
http://www.codinghorror.com/blog/2010/04/so-youd-like-to-send-some-email-through-code.html
However that is very tough to do, because you need to stay on top of SPAM standards, and abide by CAN-SPAM laws and everything else. The better bet is to use a on-demand cloud based SMTP server like this one:
Use a company that is a domain expert in the area of sending email and has gone through all the leg work to get the highest deliverability rate. And will stay on top of the standards for you, and monitor black lists for problems.