HI, I have a problem with outlook 2016 and 2019 connecting to an Exchange 2016 cu23 with the latest security patches. I have some outlook clients that have multiple mailboxes configured. There is one main user mailbox plus other service mailboxes. Only the personal mailbox is configured in cached mode. Sometimes when sending the email the error 0x80070005 is returned. I solve the error by deleting the address from the nk2 file and then the email is sent correctly. How come this problem arises? Is there a way to solve the problem permanently as it occurs randomly on multiple computers?