Hello @Kumar Parida, Rajesh
To confirm my understanding:
- You open an email that is stored in a Shared Mailbox.
- You select "Reply All".
- Outlook initially prepares the reply using the Shared Mailbox as the sender.
- You then change the "From" field from the Shared Mailbox to your own email account.
- At that point, New Outlook opens a new compose window.
- The same action works as expected in Classic Outlook.
Is this correct?
The reason I want to clarify this point is that the original email belongs to the Shared Mailbox. When "Reply All" is selected, Outlook starts the reply within the Shared Mailbox context. Changing the "From" address to your personal mailbox means Outlook must switch the sending context from the Shared Mailbox to your mailbox, so understanding exactly what happens after that change is important.
To confirm the situation and suggest the troubleshooting steps in the right direction, may I confirm a few points:
- Does the new compose window appear immediately after changing the "From" field?
- Does this happen with every email in the Shared Mailbox? (You can repeat the same test using another email from the Shared Mailbox.)
- Does the new window contain the original email conversation and recipients? Or is it a completely blank new message?

You can send me a screenshot or describe more about this issue (all personal information was removed) so I can understand your needs better for further assistance.

Looking forward to hearing from you for further assistance!
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