Errm no, a reply-to header is not the same as a sender envelope. Spam filters will flag emails that are faking the sender envelope. Spf is also only checking sender envelope. A reply-to can generally be what ever you want, same for from header... So linked sends email with from and reply-to headers set with your email, but sender envelop is from their server. So email appears to come from you, but was sent from linked in server, which is setup to pass spf test so does not get flagged by spam filter. Check the headers in the emails raw source, and you will see what i mean