I switched hosts, pointed our domains to the new host, and set up emailboxes on the new host, using the same email addresses as on the old host. Everything works perfectly, and email is sent & received by the emailboxes on the new host. So why does spam — and only spam — continue to flow into the emailboxes on the old host?
This spam does not appear in the emailboxes on the new host, only the old host.
These spammers are not sending to our email addresses in the standard way (which would land them in our emailboxes on the new host). So how are they still finding their way into the old emailboxes, which are no longer linked to our domains?
UPDATE: A friend had a similar experience, and the answer she got was that the spam was being sent from the (old/first) same server, using the DNS on the server, instead of one of the outside world DNS servers. This does make sense to me.