If you have the misfortune of having to troubleshoot and repair boot issues on a virtual machine after a physical host crash, these two commands might help you.

First of all, try to get into the advanced settings on boot (it should be the F11 key), or after a while Windows (Server or 10/11) might automatically go into the menu when it cannot boot from disk. Alternatively a Windows ISO image can be used.

Once in the advanced settings, run the good old checkdisk command:

chkdsk /f C:

After completion, restart the VM and check if you are able to boot. If the issue persists, try restoring the registry database (once again through the advanced settings or a Windows ISO). A scheduled task regularly backs up the registry and puts it the folder C:\Windows\System32\config\Regbak.

copy C:\windows\system32\config\RegBack\* C:\windows\system32\config

Restart the VM and check if you are able to boot into Windows. If you still have issues, you should consider restoring from a backup (it sucks but sometimes it is unavoidable).

If you need make a room mailbox public, for example for a public event, these few PowerShell commands will help you:

First, connect to Exchange Online with your tenant admin:

Connect-ExchangeOnline

Make the calendar public and make the calendar entries visible to everyone:

Set-MailboxCalendarFolder publicRoomMailbox:\Calendar -PublishEnabled $true

Set-MailboxCalendarFolder publicRoomMailbox:\Calendar -Detaillevel Full

Show the HTML and iCalendar URL:

Get-MailboxCalendarFolder publicRoomMailbox:\Calendar | fl published*

The URLs can be shared with anyone or the HTML URL could be embedded on a website as part of an iFrame.

In an Active Directory environment, it is best practice to enable DNS Aging and Scavenging. Aging and Scavenging will ensure that old DNS entries (such as decommissioned servers or computers) are deleted regularly. You will find this option by opening the properties in DNS Manager under the advanced tab or in the properties of a Forward Lookup Zone.

For detailed information, check out https://www.windowstechno.com/dns-aging-and-scavenging/.

If you need to change a synced AD account with an Exchange Online mailbox into a cloud-only user, these are the steps you need to take:

Move the user to an OU that is not synced by AD Connect and run a delta sync on the AD Connect server (or wait for 30 minutes):

Start-ADSyncSyncCycle -PolicyType Delta

The mailbox is now in the "Soft deleted" state, which means that it is deleted but can be restored within 30 days. To view the soft deleted mailbox run this command:

Connect-ExchangeOnline

Get-Mailbox -SoftDeletedMailbox user@ajni.it | fl guid

Now link the deleted mailbox with the cloud-only user. The cloud-only user has already been created in my case. You will need to insert the user's password in order to proceed.

New-Mailbox -InactiveMailbox 7fb16ffd-cf3a-42ef-a9d3-e0293f5ef6c2 -Alias cloudOnlyUser -MicrosoftOnlineServicesID cloudOnlyUser@ajni.onmicrosoft.com

Afterwards you can either assign a license to the user or convert that mailbox into a shared mailbox which does not need a license.

Normally, with an Office 365 mailbox, you can only send mails with the primary email address. Sending from aliases was not allowed. Microsoft recently rolled out this feature which can be enabled through Exchange Online PowerShell:

Connect-ExchangeOnline

To view the current settings:

Get-OrganizationConfig | fl SendFromAlias*

To enable the feature:

Set-OrganizationConfig -SendFromAliasEnabled $true

To view the settings again:

Get-OrganizationConfig | fl SendFromAlias*

References:

https://lazyadmin.nl/office-365/send-from-alias/