Recently one of sender authentication methods called SPF is getting popularized as an anti-spam technology. However, SPF has a problem in terms of that the forwarded e-mails can not be authenticated correctly. In this paper, we propose a solution for SPF on forwarded e-mails by tracing recipient addresses in "Received" fields of e-mail header without customization on forwarding MTA. The results of experiments on real network environment show that 88.3% of e-mails with authentication information published were authenticated successfully in the proposal method and 69.5% of e-mails which failed in the conventional SPF method were authenticated successfully in the proposal as well. Accordingly, we can confirm that the proposal method works effectively and solves the existing problem. © 2010 IEEE.