Yes I like this work, However note that due to Spammers / Virus distributors that make it their work to misuse nice backups systems like MX 20 systems to cause DoS Attacks use the MX 20 server to SPAM domains.
I will explain.
If I send mail to MX 10 about non-existing users the mail gets dropped immediately, however if I send it to the MX 20 (making as if the MX 10 is down) then all mail is queued, and the processor and bandwidth attack can continue in full force! This is one technique used commonly.
Because sending mail will be held for a couple days till the MX 10 comes alive most ISP's adopted the MX 10 and dropped all MX 20 's or other MX backups to stop this behaviour as only the MX 10 (final destination) know whether the user does exist or not.
With your Implementation of relay-recipient this can be curbed a lot. But i will use SSH [SCP] command to retreive the data secured