Why do letters hang in outbox?

Question

System administration

I am moving Windows Server 2012R2 with Exchange 2013 installed on it , from Hyper-V to KVM-Proxmox 5.1 (manually installed on Debian). I am moving by restoring from a backup of an entire server using Windows backup tools. The problem is that the Outlook 2010 client clings to the server, but the letters are not sent, they hang in the outbox. What checked:
1. Are all services running on Exchange? Services do not always start automatically, but are started manually. In addition, I tried to restart and enable all services that have automatic start. Nothing has changed.
2. Are the ports open? Connected by telnet to 143 (* OK The Microsoft Exchange IMAP4 service is ready ) and 587 ( 220 domen.ru Microsoft ESMTP MAIL service ready ) ports.
3. Are the components running? Checked with the Get-ServerComponentState command. Some components were not started, started manually. Nothing has changed.
I turn off the server on Proxmox and turn it on to Hyper-V, the mail leaves. I set the ip-addresses of the servers to be the same.
Where else to look and check?

Answer 1

possibly - replace Outlook 2010 with 2013 and above

Answer 2

Are the connector settings the same?

Answer 3

at least on Exchange, the version below was... emails in outbox == non-working Exchange Store