You need the process on how to change or move the Web Site URL in Veeam Backup Enterprise Manager.
If you change the server host name that is running IIS, move the Veeam Backup Enterprise Manager (BEM) Database to a new server with the old DB. Changes between the new Backup Enterprise Manager installation (IIS) and the old Database may result in emails being delivered incorrectly to the old Backup Enterprise Manager server.
To fix your issue:
The "dbo.Notification.MailSettings" Table in the SQL Database "VeeamBackupReporter" contains more important information that cannot be edited with the Veeam Backup Enterprise Manager itself. This includes the body of the email message. Everything else should be editable within Veeam Backup Enterprise Manager under Backup Enterprise Manager --> Configuration --> Notification.