More mailbox muddle

(If you’re all are sick of me asking about setting up mailboxes, just say and I’ll shut up! :wink: )

Tryin to set an existing address to deliver to an existing address-less mailbox, but Addresses, Mailbox Login (sic) fails to offer the mailbox. It offers m#######-style mailboxes, but not this or any other abcedfeg-style mailbox.

The page advises

if you want to forward to an existing mailbox, just enter its email address in the box above

which of course I can’t do because the mailbox is addressless and the problem above prevents me adding an address!

Any ideas, anyone? Giving up on this address/mailbox need not apply :wink: