"RT could not load a valid user" issue

We sent a reply to a customer from an existing ticket, and the
customer replied to the email. We had several hours of cron job
failures this afternoon because of “RT could not load a valid user,
and RT’s configuration does not allow for the creation of a new user
for this email (customer@example.com). You might need to grant
’Everyone’ the right ‘ReplyToTicket’ for the queue General.”

No problem, we got the cron job failures to go away by setting
ReplyToTicket privs for Everyone. The customer reply is now in place
in the ticket. But we’re still getting the following errors in our
logs after fixing that issue:

Mar 15 01:56:03 system RT: RT could not load a valid user, and RT’s
configuration does not allow for the creation of a new user for your
email. (/opt/rt3/bin/…/lib/RT/Interface/Email.pm:244)
Mar 15 01:56:03 system RT: Could not record email: Could not load a
valid user (/opt/rt3/share/html/REST/1.0/NoAuth/mail-gateway:75)

They continue to appear every time our cron job runs to collect
incoming emails. We have ReplyToTicket and CreateTicket turned on for
Everyone. We have “–queue General --action correspond” in the
argument list for rt-mailgate. We are not running LDAP. Why are we
still getting these messages, and how do we get them to stop?

Faith