550 Sender verify failed (new server)

I'm setting up a new server to replace an existing one. The new server doesn't currently have any accounts on it; once everything is configured, I'll be copying all of the accounts on the old server to this one.

In configuration, though, I've set up Edit System Mail Preferences > root's mail to point to an email address that is currently on the old server (but, of course, will soon be on the new server).

Since then, I've gotten a ton of emails (mainly from CSF) that have bounced with a 550 Sender verify failed error:

Code:

user@example.com
    (generated from root@new.server.com)
    SMTP error from remote mail server after RCPT TO:<user@example.com>:
    host example.com [123.45.67.89]: 550-Verification failed for <root@new.server.com>
    550-The mail server could not deliver mail to root@new.server.com.  The account or domain may not exist, they may be blacklisted, or missing the proper dns entries.
    550 Sender verify failed

In the above, 123.45.67.89 refers to the IP of the old server, not the new one. But new.server.com, of course, refers to the name of the new server, not the old one.

I tried adding the new server's IP to the SPF record on the old server, but that didn't seem to solve the problem (unless it needs to propogate? I only changed it about 30 minutes ago):

"v=spf1 +a +mx +123.45.67.89 +ip4:987.65.43.21 ?all"

What else do I need to change in order to make this be allowed?