In Outlook, when you want to change the sender account for a reply, it can result in a new blank email being generated, which causes the loss of the original email chain. Unfortunately, the current design of Outlook does not support switching the sender account while maintaining the email history in the same message.
To work around this, you can manually copy the email history from the original message and paste it into the new email. Alternatively, you can close the meeting request or email and switch to the calendar or email for your intended account before creating a new message.
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