We are changing the source of forwarded mail as handled by the “Mail Forwarding” option in the account control center. Messages forwarded to external email addresses were previously sent from 18.104.22.168/28. Starting today, we will begin migrating forwarding to a new group of servers out of 22.214.171.124/28. This change is permanent and is being made as part of our recent announcement on enforced content filtering for forwarded mail.
This will also allow us, in the future, to insert forwarding delivery results into the online mail logs. More immediately, these new servers will be also be IPv6 enabled.
[May 8] The IPv6 enabled servers are now online. If a forwarding destination is reachable via IPv6, we’ll try it.