Outlook Reply or ReplyAll to an Email

To simply Reply or ReplyAll selected messages try the following.

Option Explicit
Sub ReplyMSG()
    Dim olItem As Outlook.MailItem
    Dim olReply As MailItem ' Reply
    Dim olRecip As Recipient ' Add Recipient

    For Each olItem In Application.ActiveExplorer.Selection
    Set olReply = olItem.ReplyAll
    Set olRecip = olReply.Recipients.Add("Email Address Here") ' Recipient Address
        olRecip.Type = olCC
            olReply.HTMLBody = "Hello, Thank you. " & vbCrLf & olReply.HTMLBody
        olReply.Display

        'olReply.Send
    Next olItem
End Sub

To hide the recipient use BCC Example

olRecip.Type = olBcc

To add multiple recipient just add

Set olRecip = olReply.Recipients.Add("Email Here")
Set olRecip = olReply.Recipients.Add("Email Here")
Set olRecip = olReply.Recipients.Add("Email Here")

With out Recipient try the following.

Option Explicit
Sub ReplyMSG()
    Dim olItem As Outlook.MailItem
    Dim olReply As MailItem ' Reply

    For Each olItem In Application.ActiveExplorer.Selection
    Set olReply = olItem.ReplyAll
            olReply.HTMLBody = "Hello, Thank you. " & vbCrLf & olReply.HTMLBody
        olReply.Display

        'olReply.Send
    Next olItem
End Sub