Rsyslog : copy with changing the facility

I have saslauthd with save the logs in LOG_AUTH in our rsyslogd server. It can't be changed without recompiling, and I don't want to do that. I would like to see all the LOG_AUTH in LOG_MAIL, because I do an export to an external machine, and I would like to see all the saslauthd logs in LOG_MAIL in the distant server. Of course, in local I can add "auth.* " in the mail.log file section, but the export will not be in the right file because I filter in export by syslog Facility/Priority.

How can I export all the AUTH logs into MAIL logs ?

Thanks