What is the "safest" way to allow an external host to relay e-mail through our Ironport? I know it's not "recommended", but I don't have any choice. I guess I could set up the external IP that's allowed to relay in Mail Policies --> Hat Overview - Relaylist. But that would allow anyone from that IP to relay, and I don't really feel that it's secure enough. Is it anyway to "tighten" the security and also require a username/password in combination with coming for the correct IP-address to make it atleast a little bit more safe?
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