Decomission of an old Exchange 2013 server

Hello everyone. I have a messy situation here. We contracted a small IT company to help us migrate from Ex2007 to Ex2019. I trusted them because they said they'd had experience upgrading Exchange. First they moved it to intermediary Ex2013 (named MAIL) and then finally to Ex2019 (named EMS01). Now, the server works okay for the most part, but I decided to read up on this topic and realized they had completely failed to decommission the Ex2007 properly. They just told me to remove it from AD which I did. On top of that they gave the Ex2019 the same name as Ex2007. So that’s not good and I probably will have to deal with that at some point.

For now I’m faced with the problem of decommissioning the Ex2013 (MAIL) but I definitely don't want to go to those guys again (and I'm very reluctant to trust anyone else to do the job at this point). So I decided it might be better to do it myself with a lot of help from this great community. I went through Exchange Deployment Assistant and also this article from Exchange Team blog and performed some of the checks before decommissioning and right from the get go I have some problems indicating that those guys didn’t do a great job at migrating either.

Things I’ve noticed:

• In 'migration' there are a couple of batches that have errors: one is a mailbox of the admin account that was used to move Exchange and the other is arbitration mailbox. Running Remove-MigrationBatch with -WhatIf parameter doesn’t return any errors though.
• In Ex2019 EAC there are two servers listed and two DBs (actually three, there’s also a dismounted DB with a non-descriptive name). The old server still had it’s own Autodiscover URI, I deleted it.
• MAIL is still listed in our internal DNS. There was also an (A) record in our external DNS, I removed it.
• Clients still look for OAB on the old server.

Here are the checks I did (slightly redacted):

[PS] C:\>Get-MailboxDatabase | Format-Table Name,Server,OfflineAddressBook -Auto

Name                        Server OfflineAddressBook
----                        ------ ------------------
exchange13database          MAIL
Mailbox Database 1765469630 EMS01
exchange16database          EMS01


[PS] C:\>Get-ExchangeServer

Name                ServerRole  Edition     AdminDisplayVersion
----                ----------  -------     -------------------
MAIL                Mailbox     Enterprise  Version 15.0 (Bu...
EMS01               Mailbox     Enterprise  Version 15.2 (Bu...


[PS] C:\>Get-Mailbox "Migration.8f3e7716-2011-43e4-96b1-aba62d229136" -Arbitration | Format-List Name,Database,ServerName,AdminDisplayVersion


Name                : Migration.8f3e7716-2011-43e4-96b1-aba62d229136
Database            : exchange13database
ServerName          : mail
AdminDisplayVersion : Version 15.0 (Build 1497.2)



[PS] C:\>Get-Mailbox -Arbitration | Format-List Name,Database,ServerName,AdminDisplayVersion


Name                : SystemMailbox{1f05a927-876a-49e7-b208-e00c8b42248f}
Database            : exchange16database
ServerName          : ems01
AdminDisplayVersion : Version 15.2 (Build 221.12)

Name                : SystemMailbox{bb558c35-97f1-4cb9-8ff7-d53741dc928c}
Database            : exchange16database
ServerName          : ems01
AdminDisplayVersion : Version 15.2 (Build 221.12)

Name                : SystemMailbox{e0dc1c29-89c3-4034-b678-e6c29d823ed9}
Database            : exchange16database
ServerName          : ems01
AdminDisplayVersion : Version 15.2 (Build 221.12)

Name                : Migration.8f3e7716-2011-43e4-96b1-aba62d229136
Database            : exchange13database
ServerName          : mail
AdminDisplayVersion : Version 15.0 (Build 1497.2)

Name                : FederatedEmail.4c1f4d8b-8179-4148-93bf-00a95fa1e042
Database            : exchange16database
ServerName          : ems01
AdminDisplayVersion : Version 15.2 (Build 221.12)

Name                : SystemMailbox{D0E409A0-AF9B-4720-92FE-AAC869B0D201}
Database            : Mailbox Database 1765469630
ServerName          : ems01
AdminDisplayVersion : Version 15.2 (Build 221.12)

Name                : SystemMailbox{2CE34405-31BE-455D-89D7-A7C7DA7A0DAA}
Database            : Mailbox Database 1765469630
ServerName          : ems01
AdminDisplayVersion : Version 15.2 (Build 221.12)



[PS] C:\>Get-ExchangeServer | Where {($_.AdminDisplayVersion -Like "Version 15.0*") -And ($_.ServerRole -Like "*ClientAccess*")} | Get-ClientAccessServer | Format-Table Name,AutoDiscoverServiceInternalUri -Auto
[PS] C:\>Get-ExchangeServer | Where {($_.AdminDisplayVersion -Like "Version 15.2*") -And ($_.ServerRole -Like "*Mailbox*")} | Get-ClientAccessService | Format-Table Name,AutoDiscoverServiceInternalUri -Auto

Name  AutoDiscoverServiceInternalUri
----  ------------------------------
EMS01 https://ems01.xxxxxx.local/Autodiscover/Autodiscover.xml


[PS] C:\>Get-SendConnector | Format-Table Name, SourceTransportServers -AutoSize

Name     SourceTransportServers
----     ----------------------
xxxxxx.ru {EMS01, MAIL}
Internet {}


[PS] C:\>Get-ForeignConnector | Format-Table Name, SourceTransportServers -Autosize
[PS] C:\>Get-ReceiveConnector -Server MAIL

Identity                          Bindings       Enabled
--------                          --------       -------
MAIL\Client Proxy MAIL            {0.0.0.0:465}  True
MAIL\Default Frontend MAIL        {0.0.0.0:25}   True
MAIL\Outbound Proxy Frontend MAIL {0.0.0.0:717}  True
MAIL\Client Frontend MAIL         {0.0.0.0:587}  True
MAIL\Default MAIL                 {0.0.0.0:2525} True


[PS] C:\>Set-ADServerSettings -ViewEntireForest $True
[PS] C:\>Get-Mailbox -Server MAIL -ResultSize Unlimited
[PS] C:\>Get-Mailbox -Server MAIL -Archive -ResultSize Unlimited
[PS] C:\>Get-SiteMailbox
[PS] C:\>Get-SiteMailbox -DeletedSiteMailbox
[PS] C:\>Get-Mailbox -Server MAIL -PublicFolder -ResultSize unlimited
[PS] C:\>Get-MoveRequest -ResultSize Unlimited | Remove-MoveRequest -Confirm:$false -WhatIf
[PS] C:\>Get-MigrationBatch | Remove-MigrationBatch -Confirm:$false -WhatIf
WhatIf: Удалить пакет миграции "1-13"?
WhatIf: Удалить пакет миграции "14-28"?
WhatIf: Удалить пакет миграции "3"?
WhatIf: Удалить пакет миграции "123"?
WhatIf: Удалить пакет миграции "4"?
WhatIf: Удалить пакет миграции "5"?
WhatIf: Удалить пакет миграции "6"?
WhatIf: Удалить пакет миграции "7"?
[PS] C:\>Get-Mailbox -ResultSize unlimited | Where-Object {$_.AdminDisplayVersion -like "Version 15.0*"}
[PS] C:\>