To move encrypted emails, use the Copy and Delete methods instead of Move. Here’s a quick code example:

Sub MoveEncryptedEmails()
    Dim sourceFolder As Outlook.MAPIFolder
    Dim targetFolder As Outlook.MAPIFolder
    Dim item As Object
    Set sourceFolder = Application.Session.GetDefaultFolder(olFolderInbox)
    Set targetFolder = Application.Session.Folders("YourTargetFolder")
    For Each item In sourceFolder.Items
        If item.Class = olMail And item.PropertyAccessor.GetProperty("http://schemas.microsoft.com/ _
            mapi/proptag/0x7D01001E") = "IPM.Note.SMIME.MultipartSigned" Then
            item.Copy targetFolder
            item.Delete
        End If
    Next
End Sub
Replace "YourTargetFolder" with your actual target folder name.