Outlook插件开发：回复全部时检测Bcc触发警告

1. 捕获“回复全部”事件 #

要触发回复全部的处理逻辑，需订阅Outlook MailItem 的 ReplyAll 事件。通过监听Explorer的选中项变化，对当前选中的邮件绑定事件：

Imports Outlook = Microsoft.Office.Interop.Outlook

Public Class ThisAddIn
    Private WithEvents currentMail As Outlook.MailItem

    Private Sub ThisAddIn_Startup() Handles Me.Startup
        AddHandler Application.ActiveExplorer.SelectionChange, AddressOf Explorer_SelectionChange
    End Sub

    Private Sub Explorer_SelectionChange()
        ' 清除之前绑定的事件，避免内存泄漏
        If currentMail IsNot Nothing Then
            RemoveHandler currentMail.ReplyAll, AddressOf MailItem_ReplyAll
            currentMail = Nothing
        End If

        ' 获取当前选中的单封邮件
        Dim selection As Outlook.Selection = Application.ActiveExplorer.Selection
        If selection.Count = 1 AndAlso TypeOf selection(1) Is Outlook.MailItem Then
            currentMail = CType(selection(1), Outlook.MailItem)
            AddHandler currentMail.ReplyAll, AddressOf MailItem_ReplyAll
        End If
    End Sub

    Private Sub MailItem_ReplyAll(ByVal Response As Object, ByRef Cancel As Boolean)
        ' 回复全部触发时执行检测逻辑
    End Sub

2. 检测原邮件中用户是否在Bcc列表 #

在MailItem_ReplyAll事件中，直接操作原邮件对象currentMail（而非生成的回复草稿Response），遍历收件人集合判断当前用户是否在Bcc组：

Private Sub MailItem_ReplyAll(ByVal Response As Object, ByRef Cancel As Boolean)
    Dim currentUserEmail As String = Application.Session.CurrentUser.Address
    Dim isInBcc As Boolean = False

    ' 遍历原邮件的所有收件人
    For Each recip As Outlook.Recipient In currentMail.Recipients
        If recip.Type = Outlook.OlMailRecipientType.olBCC Then
            ' 匹配邮箱地址（可按需调整为匹配显示名称）
            If recip.Address.Equals(currentUserEmail, StringComparison.OrdinalIgnoreCase) Then
                isInBcc = True
                Exit For
            End If
        End If
    Next

    If isInBcc Then
        ' 弹出警告提示
        MsgBox("注意：你是原邮件的密送收件人，回复全部可能会暴露你的身份！", MsgBoxStyle.Exclamation)
    End If
End Sub

额外提示 #

• 右键菜单、快捷键触发的回复全部操作，上述事件同样能捕获；
• 若需处理Exchange环境下的地址格式差异，可使用recip.AddressEntry.GetExchangeUser().PrimarySmtpAddress获取标准SMTP地址；
• 若要阻止默认回复全部行为，可将Cancel参数设为True。

内容的提问来源于stack exchange，提问作者ThaiDorito