簡單高效。具備“必需”以及獨特的功能，這些控件幫助開發人員簡單快速地將復雜的電子郵件功能添加到他們的應用程序中。
本文主要介紹了SMTP服務器退回郵件的代碼示例。目前MailBee.NET Objects在線訂購享75折優惠正在進行中，歡迎您下載試用版進行運用！
在上期的SMTP部分中，我們將退回的電子郵件發送到指定的單個電子郵件地址。
每封退回的電子郵件都包含失敗的電子郵件地址（以及其他信息）。這個失敗的地址是我們想知道的。這個任務看起來很簡單 - 你需要做的是掃描退回的
郵件以確定地址的典型字段。但是有一個隱藏的危險：每個郵件服務器都有自己的郵件退回格式。雖然它們幾乎具有相同的“From”和“主題”字段，但是退回地址可以在郵件的任何位置。MailEnable服務器的典型退回郵件如下所示：
From: POSTMASTER@domain.com
To: jdoe@domain.com
Subject: Message Delivery Failure
MailEnable: Message Delivery Failure.
The following recipient(s) could not be reached:
Recipient: [SMTP: bill@domain.com] Reason: The message could not be delivered because the domain name (domain.com) does not appear
to be registered.
函數GetInvalidEmailAddressME（）檢查郵件是否被退回，并從退回的郵件中提取失敗的地址。由于退回郵件格式不同，此功能僅對MailEnable服務器有效。例如，如果你正在使用Communigate Pro服務器，則退回消息如下所示：
From: MAILER-DAEMON@domain.local
To: jdoe@localhost Subject:
Undeliverable mail:
Failed to deliver to '<bill@localhost>'
正如你所看到的，這個退回的郵件與前一個幾乎相同。使用哪個服務器并不重要，退回信息總是有From，To和Subject字段，退回信息在其正文中有失敗的地址。函數GetInvalidEmailAddressCP（）與前一個函數幾乎相同; 區別僅在于檢查郵件字段并搜索失敗的地址。支持盡可能多的退回電子郵件格式至關重要。這就是為什么你需要修改GetInvalidEmailAddress（）函數，以適應服務器使用的退回電子郵件格式。
注意：在某些情況下，你可能需要掃描退回的電子郵件以獲取其他信息。如果由于暫時的問題，退回的郵件到達，則不要刪除電子郵件地址：郵箱超過配
額，郵件服務器關閉等。退回郵件可以分為兩種類型：硬郵件和軟郵件。如果是不存在的帳戶或域，則會發生硬性退回。其他故障，如完整的郵箱或暫時
不可用的域，則是軟性退回。你可以為數據庫中的每個地址進行計算。也許下一次嘗試發送郵件到具有一些軟性退回的地址時將成功。
代碼示例：
在此示例中，我們從指定的帳戶中檢索退回的電子郵件，然后從每個退回的電子郵件中提取失敗的電子郵件地址。失敗的地址傳遞給RemoveEmailFromDatabase子程序，該子程序必須從數據庫中刪除失敗的地址。應用程序還會從服務器中刪除退回的電子郵件，以避免下次處理。
C#：
// Create POP3 object
Pop3 pop = new Pop3();
// Enable logging to file
pop.Log.Enabled = true;
pop.Log.Filename = @"C:\log.txt";
pop.Log.Clear();
// Connect to POP3 server
pop.Connect("mail.domain.com");
pop.Login("bounce", "secret");
// Download headers and bodies of all messages.
MailMessageCollection msgs = pop.DownloadMessageHeaders(1, -1, -1);
// Loop through all messages in the mailbox
foreach (MailMessage msg in msgs)
{
string strLine = msg.BodyPlainText;
Console.WriteLine("From: " + msg.From.Email);
// Get failed email address
string str_invalid_email = GetInvalidEmailAddressME(msg);
// If str_invalid_email is non-empty then failed email
// address was found
if (str_invalid_email.Length > 0)
{
// Remove failed email from database
RemoveEmailFromDatabase(str_invalid_email);
// Display invalid adress
Console.WriteLine("Invalid email: " + str_invalid_email);
// Delete bounced email from server to avoid
// processing it next time
pop.DeleteMessage(msg.IndexOnServer);
}
}
// Disconnect from POP3 server
pop.Disconnect();
// The function checks whether the message is bounced and extracts
// failed address
// from bounced message. Valid only for MailEnable servers
static string GetInvalidEmailAddressME(MailMessage msg)
{
string str_invalid_email = msg.BodyPlainText;
// Check if this is a bounced message report
if (msg.Subject.IndexOf("Delivery Failure") == -1)
{
return "";
}
if (msg.From.ToString().IndexOf("POSTMASTER") == -1)
{
return "";
}
// Now we're sure this is a bounced message report
int i_start;
i_start = str_invalid_email.IndexOf("SMTP:");
// Check if bounced message report contains "Recipient:" field
if (i_start == -1)
{
return "";
}
// Get failed address
i_start += 5;
i_end = str_invalid_email.IndexOf("]",i_start);
str_invalid_email.Substring(i_start, i_end);
return str_invalid_email;
}
// The function checks whether the message is bounced and extracts
// failed address
// from bounced message. Valid only for Communigate Pro servers
static string GetInvalidEmailAddressCP(MailMessage msg)
{
string str_invalid_email = msg.BodyPlainText;
// Check if this is a bounced message report
if (msg.Subject.IndexOf("Undeliverable mail") == -1)
{
return "";
}
if (msg.From.ToString().IndexOf("MAILER-DAEMON") == -1)
{
return "";
}
// Now we're sure this is a bounced message report
int i_start;
i_start = str_invalid_email.IndexOf("to '<");
// Check if bounced message report contains
// "Failed to deliver to " field
if (i_start == -1)
{
return "";
}
// Get failed address
i_start += 5;
i_end = str_invalid_email.IndexOf("]",i_start);
str_invalid_email.Substring(i_start, i_end);
return str_invalid_email;
}
// This function must remove (or disable) specified
// email address from mailing list
static void RemoveEmailFromDatabase(string str_invalid_email)
{
// TODO: Add your code here
}
VB.NET:
Dim pop As New Pop3
' Enable logging to file
pop.Log.Enabled = True
pop.Log.Filename = "C:\log.txt"
pop.Log.Clear()
' Connect to POP3 server
pop.Connect("mail.domain.com")
pop.Login("jdoe", "secret")
' Download headers and bodies for all messages.
Dim msgs As MailMessageCollection = pop.DownloadMessageHeaders(1, -1, -1)
' Loop through all messages in the mailbox
Dim msg As MailMessage
For Each msg In msgs
Dim strLine As String = msg.BodyPlainText
Console.WriteLine("From: " + msg.From.Email)
' Get failed email address
Dim str_invalid_email As String = GetInvalidEmailAddressME(msg)
' If str_invalid_email is non-empty then failed email
' address was found
If str_invalid_email.Length > 0 Then
'Remove failed email from database
RemoveEmailFromDatabase(str_invalid_email)
' Display invalid address
Console.WriteLine("Invalid email: " & str_invalid_email)
' Delete bounced email from server to avoid
' processing it next time
pop.DeleteMessage(msg.IndexOnServer)
End If
Next
Console.ReadLine()
' Disconnect from POP3 server
pop.Disconnect()
' The function checks whether the message is bounced and extracts
' failed address
' from bounced message. Valid only for MailEnable servers
Function GetInvalidEmailAddressME(ByVal msg As MailMessage) As String
Dim str_invalid_email As String = msg.BodyPlainText
' Check if this is a bounced message report
If msg.Subject.IndexOf("Delivery Failure") = -1 Then
Return ""
End If
If msg.From.ToString().IndexOf("POSTMASTER") = -1 Then
Return ""
End If
' Now we're sure this is a bounced message report
Dim i_start As Integer, i_end As Integer
i_start = str_invalid_email.IndexOf("SMTP:")
' Check if bounced message report contains "Recipient:" field
If i_start = -1 Then
Return ""
End If
' Get failed address
i_start += 5
i_end = str_invalid_email.IndexOf("]", i_start)
str_invalid_email.Substring(i_start, i_end)
Return str_invalid_email
End Function
' The function checks whether the message is bounced and extracts
' failed address
' from bounced message. Valid only for Communigate Pro servers
Function GetInvalidEmailAddressCP(ByVal msg As MailMessage) As String
Dim str_invalid_email As String = msg.BodyPlainText
' Check if this is a bounced message report
If msg.Subject.IndexOf("Undeliverable mail") = -1 Then
Return ""
End If
If msg.From.ToString().IndexOf("MAILER-DAEMON") = -1 Then
Return ""
End If
' Now we're sure this is a bounced message report
Dim i_start As Integer, i_end As Integer
i_start = str_invalid_email.IndexOf("to '<")
' Check if bounced message report contains
' "Failed to deliver to " field
If i_start = -1 Then
Return ""
End If
' Get failed address
i_start += 5
i_end = str_invalid_email.IndexOf("]", i_start)
str_invalid_email.Substring(i_start, i_end)
Return str_invalid_email
End Function
' This function must remove (or disable) specified
' email address from mailing list
Sub RemoveEmailFromDatabase(ByVal str_invalid_email As String)
' TODO: Add your code here
End Sub
標簽：
電子郵件
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