I get duplicate emails like crazy. My solution is to set aside a special folder in my email service for SDMB messages and automatically route all messages from “webmaster@straightdope.com” to the SDMB folder. Depending on your e-mail service you may or may not have this option, but I do believe most email client programs and webmail services support this.
Once all the SDMB messages are set aside I can delete the ones that are duplicates.