VB.NET

Fetch a Chunk of Messages, Tracking Failures

Demonstrates the Chilkat Imap.FetchChunk2 method, which downloads a run of messages by sequence number and reports which succeeded and which failed. The arguments are the starting sequence number, the count, a MessageSet that receives the failed IDs, a MessageSet that receives the successfully-fetched IDs, and the EmailBundle. This example fetches the first chunk of messages and reports the success and failure counts.

Background: When bulk-downloading a large mailbox, individual messages can occasionally fail to fetch (a corrupt message on the server, a transient error) without failing the whole operation. FetchChunk2 is designed for that reality: it returns a partial EmailBundle plus two MessageSet objects so your code can log or retry exactly the messages that did not come through, rather than aborting the entire sync.

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Dim success As Boolean = False

'  Demonstrates the Imap.FetchChunk2 method, which downloads a run of messages by sequence
'  number and reports which succeeded and which failed.  The 1st argument is the starting
'  sequence number, the 2nd is the count, the 3rd receives the failed IDs, the 4th receives
'  the successfully-fetched IDs, and the 5th is the EmailBundle.

Dim imap As New Chilkat.Imap

imap.Ssl = True
imap.Port = 993

success = imap.Connect("imap.example.com")
If (success = False) Then
    Debug.WriteLine(imap.LastErrorText)
    Exit Sub
End If

success = imap.Login("user@example.com","myPassword")
If (success = False) Then
    Debug.WriteLine(imap.LastErrorText)
    Exit Sub
End If


Dim numMessages As Integer = imap.SelectMailbox("Inbox")
If (numMessages < 0) Then
    Debug.WriteLine(imap.LastErrorText)
    Exit Sub
End If


'  Fetch messages 1..25 (or fewer if the mailbox is smaller).
Dim count As Integer = 25
If (count > numMessages) Then
    count = numMessages
End If


Dim failedSet As New Chilkat.MessageSet
Dim fetchedSet As New Chilkat.MessageSet
Dim bundle As New Chilkat.EmailBundle
success = imap.FetchChunk2(1,count,failedSet,fetchedSet,bundle)
If (success = False) Then
    Debug.WriteLine(imap.LastErrorText)
    Exit Sub
End If


Debug.WriteLine("Fetched: " & fetchedSet.Count)
Debug.WriteLine("Failed:  " & failedSet.Count)

success = imap.Disconnect()
If (success = False) Then
    Debug.WriteLine(imap.LastErrorText)
    Exit Sub
End If