Download parts of email message

Sometimes you know you’ll receive large size emails, but you only need to access some email parts, without downloading entire email messages from IMAP server.

Mail.dll .NET IMAP library allows you to download only needed parts of the specified message.

First you need to download structure of the email message. There are two methods for that: GetBodyStructureByUID and GetBodyStructureByNumber.

You can also use GetMessageInfoByUID or GetMessageInfoByNumber methods. Both methods return more information about most common email fields, such as: subject, from, to and other headers, and also include BodyStructure in their response.

BodyStructure class contains information about plain text, html, and all attachments that were added to the message. It does not contain any data though. That’s the reason why, downloading it is very fast.

To download text parts of the email (like HTML or plain text) you can use: GetTextByUID or GetTextByNumber methods of Imap class.

To download binary attachments use GetDataByUID or GetDataByNumber methods of Imap class.

Here’s the full sample for this feature:

// C#

using(Imap imap = new Imap())
{
	imap.ConnectSSL("imap.server.com");
	imap.UseBestLogin("user", "password");

	imap.SelectInbox();
	List<long> uidList = imap.Search(Flag.Unseen);
	foreach (long uid in uidList)
	{
		// Get the structure of the email
		BodyStructure structure = imap.GetBodyStructureByUID(uid);

		// Download only text and html parts
		string text, html;

		if (structure.Text != null)
		    text = imap.GetTextByUID(structure.Text);
		if (structure.Html != null)
		    html = imap.GetTextByUID(structure.Html);

		Console.WriteLine(text);
		Console.WriteLine(html);

		// Show all attachments' names
		foreach(MimeStructure attachment in structure.Attachments)
		{
			Console.WriteLine(attachment.SafeFileName);
			// You can also download entire attachment
			byte[] bytes = imap.GetDataByUID(attachment);
		}
	}
	imap.Close();
}

' VB.NET

Using imap As New Imap()
	imap.ConnectSSL("imap.server.com")
	imap.UseBestLogin("user", "password")

	imap.SelectInbox()
	Dim uidList As List(Of Long) = imap.Search(Flag.Unseen)
	For Each uid As Long In uidList
		' Get the structure of the email
		Dim struct As BodyStructure = imap.GetBodyStructureByUID(uid)

		' Download only text and html parts
		Dim text As String, html As String

		If [structure].Text IsNot Nothing Then
		    text = imap.GetTextByUID([structure].Text)
		End If
		If [structure].Html IsNot Nothing Then
		    html = imap.GetTextByUID([structure].Html)
		End If

		Console.WriteLine(text)
		Console.WriteLine(html)

		' Show all attachments' names
		For Each attachment As MimeStructure In struct.Attachments
			Console.WriteLine(attachment.SafeFileName)
			' You can also download entire attachment
			Dim bytes As Byte() = imap.GetDataByUID(attachment)
		Next
	Next
	imap.Close()
End Using

Tags: Attachments C# IMAP IMAP component VB.NET