Comment 4 for bug 1154004

Not always, just in the context of a mailing list...
The "From" can be fake, the "Sender" too but perhaps a bit less likely (spammers "on behalf of" usually fake one of the two but not both); "Sender" AFAIK can be not set so it can't be required. Is there a configuration to ask that both "From" and "Sender" are subscribed addresses, except in the case "Sender" is not set?