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prasad Challa
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Posted: 24 May 2004 at 5:41pm | IP Logged Quote prasad Challa

Hello,

I am using Mailbee's pop3 object, how do i restrict my RetrieveMessages method to pnly new messages.

Thanks
prasad challa
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Alex
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Posted: 25 May 2004 at 5:24am | IP Logged Quote Alex

Basically, the POP3 protocol has no features to determine whether a message is new or not.

However, the POP3 protocol allows you to get list of Unique-ID's of all messages in the mailbox.

The procedure is as follows:

On every connection to POP3 server, get list of Unique-ID's of all messages in the mailbox.

Then, check which of these ID's are already in database. Those ID's which already in database, correspond to old messages. If particular ID is not in database, it is a new message: download it completely!

Once all new messages are retrieved, update database with recent version of Unique-ID's list.

Thus, on very first connection the database is empty (and all messages are new). Next times the procedure will retrieve only new messages.

To get list of Unique-ID's, use Search method of POP3 object.

Sample code below shows MailBee part of the procedure discussed above. IsNewMessage function is empty, in your code it should actually lookup passed Unique-ID value in the database.

' This is main function. It retrieves new messages from
' the POP3 server and shows "Subject:" field of each
' retrieved message.
Sub RetrieveNewMessages()
Dim objPOP3, objMsg, I

' Array of Unique-IDs (taken from the POP3 server)
Dim arrIDs

' Create POP3 object
Set objPOP3 = CreateObject("MailBee.POP3")

' Unlock POP3 object
objPOP3.LicenseKey = "put your license key here"

' Set POP3 server name
objPOP3.ServerName = "mail.server.com"

' Set user credentials
objPOP3.UserName = "username"
objPOP3.Password = "password"

' Connect to the server and log in the mailbox
If objPOP3.Connect Then

    ' Get Unique-IDs for all messages in the mailbox
    arrIDs = objPOP3.Search

    ' Iterate through all messages in the mailbox
    For I = 1 To objPOP3.MessageCount

      ' Search Unique-ID of the message in the database
      If IsNewMessage(arrIDs(I)) Then
      
        ' Download new message entirely
        Set objMsg = objPOP3.RetrieveSingleMessage(I)
       
        ' Display the message's Subject
        MsgBox objMsg.Subject
      End If
    Next

    ' Close the connection
    objPOP3.Disconnect
Else
    ' Display error information
    MsgBox "Error #" & objPOP3.ErrCode
    MsgBox "Server response: " & objPOP3.ServerResponse
End If
End Sub

' This helper function should lookup the ID in the
' database, and then return True if the ID does not
' exist in the list of already downloaded messages.
Function IsNewMessage(ID)
' For demo purposes, the function always returns True.
IsNewMessage = True
End Function
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21323
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Posted: 14 September 2004 at 8:55pm | IP Logged Quote 21323

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Alex
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Posted: 15 September 2004 at 6:01am | IP Logged Quote Alex

Could you describe in more detail what did you mean?

Regards,
Alex
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juris
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Posted: 06 February 2017 at 3:01pm | IP Logged Quote juris

Alex wrote:
Basically, the POP3 protocol has no features to determine whether a message is new or not.

However, the POP3 protocol allows you to get list of Unique-ID's of all messages in the mailbox.

The procedure is as follows:

On every connection to POP3 server, get list of Unique-ID's of all messages in the mailbox.

Then, check which of these ID's are already in database. Those ID's which already in database, correspond to old messages. If particular ID is not in database, it is a new message: download it completely!

Once all new messages are retrieved, update database with recent version of Unique-ID's list.

Thus, on very first connection the database is empty (and all messages are new). Next times the procedure will retrieve only new messages.

To get list of Unique-ID's, use Search method of POP3 object.

Sample code below shows MailBee part of the procedure discussed above. IsNewMessage function is empty, in your code it should actually lookup passed Unique-ID value in the database.

' This is main function. It retrieves new messages from
' the POP3 server and shows "Subject:" field of each
' retrieved message.
Sub RetrieveNewMessages()
Dim objPOP3, objMsg, I

' Array of Unique-IDs (taken from the POP3 server)
Dim arrIDs

' Create POP3 object
Set objPOP3 = CreateObject("MailBee.POP3")

' Unlock POP3 object
objPOP3.LicenseKey = "put your license key here"

' Set POP3 server name
objPOP3.ServerName = "mail.server.com"

' Set user credentials
objPOP3.UserName = "username"
objPOP3.Password = "password"

' Connect to the server and log in the mailbox
If objPOP3.Connect Then

    ' Get Unique-IDs for all messages in the mailbox
    arrIDs = objPOP3.Search

    ' Iterate through all messages in the mailbox
    For I = 1 To objPOP3.MessageCount

      ' Search Unique-ID of the message in the database
      If IsNewMessage(arrIDs(I)) Then
      
        ' Download new message entirely
        Set objMsg = objPOP3.RetrieveSingleMessage(I)
       
        ' Display the message's Subject
        MsgBox objMsg.Subject
      End If
    Next

    ' Close the connection
    objPOP3.Disconnect
Else
    ' Display error information
    MsgBox "Error #" & objPOP3.ErrCode
    MsgBox "Server response: " & objPOP3.ServerResponse
End If
End Sub

' This helper function should lookup the ID in the
' database, and then return True if the ID does not
' exist in the list of already downloaded messages.
Function IsNewMessage(ID)
' For demo purposes, the function always returns True.
IsNewMessage = True
End Function


Hello Alex,

This method is not safe because some email servers change Uids after new configuration. Any other ideas?

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Alex
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Posted: 07 February 2017 at 12:16am | IP Logged Quote Alex

The purpose of UIDs is to keep persistent. If they change, this defeats the whole idea of them. All email will be considered new again. This sometimes happens with mail migrations - someone moves email to a new server and then Outlook (or any other POP3 client) reads all mail from the new server again thinking it's all new. That's why it's so important to keep UIDs untouched when mail migrations occur. If the server still does it - yes, all mail will be considered new. There is no workaround for that.

Regards,
Alex
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juris
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Posted: 07 February 2017 at 12:38am | IP Logged Quote juris

Hello Alex,

The solution is to not use Uids.
I prefer to download all the headers from the server.
Then I search in my database to see if there is already an email with the same date of receipt and with the same messageID.
This method is a little slower but it is much safer.


Get MyUniqueIDs for all messages in the mailbox
Code:

private Regex RegularFileNameExpression = new Regex(string.Format("[{0}]", Regex.Escape(new string(Path.GetInvalidFileNameChars()) + new string(Path.GetInvalidPathChars()))));

string MyUniqueIDs = RegularFileNameExpression.Replace(msg.Date.ToString("yyyyMMddHHmmssfff") + "_" + msg.MessageID + ".eml", "");


What do you think about it?

Regards, Lello
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Alex
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Posted: 07 February 2017 at 12:41pm | IP Logged Quote Alex

As I said earlier, UID-based method is the only one which was ever tested and found to be working. If you found another method which suits your needs, that's fine then.

Regards,
Alex
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juris
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Posted: 11 February 2017 at 3:13am | IP Logged Quote juris

Hello Alex

Server POP3 and server IMAP have different Uids for the same email.
Using Uids I risk of downloading twice the same email
Better to create a different identifier (eg: the date of receipt + MessageID)

Lello
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