(1) Predefined registration details.
Forwarding information registers in the same way as described in "Receive and reply without anonymization" above, However, enable the "Keep sender secret" setting.

(2) Anonymize email sender address and receive email.
The recipient "C" of the mail tell the "Known address" "B" to the sender instead of his own address, and receives the mail through the "Known address" "B".
In the forwarded mail, "SafetyAnswer" generates a unique anonymized address "X" corresponding to the address "A", and rewrites the sender address "A" to "X", and it will be forwarded to "C".
This anonymized address "X" generates a unique address that is completely different from "A".

(3) Reply (or send) mail from a secret email address to an anonymous address.
The mail recipient "C" sends a mail to the anonymous address "X".
Reply processing department of "SafetyAnswer" receives a reply mail addressed to the anonymous address "X".
Since the sender of the received mail is "C" and the destination is the anonymous address "X", the "SafetyAnswer" that received the reply mail has decide "A" as the destination of the final reply mail.
And new sender is determined to be "B", and mail is sent from the "Known address" "B" in the correct procedure.

(4) Receive email from "Known address".
The mail sender "A" will receive the mail sent by the mail replier "C" as the mail with the "Known address" "B" as the mail sender.
"A" sends an email to "B" and receives a reply from "B", and the presence of "C" is kept secret.
In addition, since "A" is not known to "C", the sender "A" and the receiver "C" send and receive mail through the "known address" "B" to unknown each other's address. And we can exchange emails without having to each other's address.
* In this case, "C" can reply mail by either sending or replying.
In the forwarded email from "SafetyAnswer", the sender address "A" described in the text of the email body is rewritten to the anonymous address "X". And in the reply email, the replier address "C" described in the text of the email body is rewritten to the "Known address" "B". (However, only when the mail text is correctly analyzed)