Save all attachments to disk using IMAP

Unlock the potential of efficient email processing in .NET with this comprehensive guide on saving email attachments using Mail.dll’s IMAP component and IMAP protocol.

In this article, we’ll walk you through the step-by-step process of downloading email messages using Mail.dll’s IMAP component and, more importantly, demonstrate how to effortlessly save all attachments to your disk.

Email MIME structure

The first thing you need to know is that email attachments are tightly integrated with the email message itself, ensuring that they are conveniently stored and transport together.

In MIME (Multipurpose Internet Mail Extensions), email attachments are stored together with an email message to ensure a structured and standardized way of transmitting and receiving email content with multiple parts.

The primary reason for storing attachments within the email message is to maintain a single cohesive entity that encapsulates all the components of the email, including its text, formatting, and any attached files. By bundling attachments with the message, the entire email becomes a self-contained package, making it easier to handle and process by email clients and servers.

Attachments in Mail.dll

Invoking Imap.GetMessageByUID method is going to download entire email message, including all attachments.

Attachments are stored within the email as part of a mime tree. Usually Quoted-Printable or Base64 encoding is used.

However, with Mail.dll, you don’t need to worry about navigating this mime tree yourself. The library efficiently parses the email’s structure, effortlessly exposing all attachments as familiar .NET collections. This user-friendly approach simplifies the process of handling email attachments, allowing you to focus on building robust and efficient email management solutions with ease.

There are 4 collections that contain attachments:

• IMail.Attachments – all attachments (includes Visuals, NonVisuals and Alternatives).
• IMail.Visuals – visual elements, files that should be displayed to the user, such as images embedded in an HTML email.
• IMail.NonVisuals – non visual elements, “real” attachments.
• IMail.Alternatives – alternative content representations, for example ical appointment.

How to download all email attachments in .NET

To retrieve all attachments from an email, you can take advantage of the IMail.Attachments collection provided by Mail.dll. This collection serves as a comprehensive repository, housing all the attachments associated with the email.

Each attachment is represented by a dedicated MimeData object, which encapsulates the specific data and metadata of the attachment.

Using the IMail.Attachments collection eliminates the need for manual traversal of the email’s mime tree or deciphering complex structures. Instead, Mail.dll handles the heavy lifting for you, ensuring a streamlined and user-friendly experience when accessing email attachments programmatically.

Installation

The easiest way to install Mail.dll is to download it from nuget via Package Manager:

PM> Install-Package Mail.dll

Alternatively you can download Mail.dll directly from our website.

Download emails and all attachments

The C# code to download all emails and save all attachments using Mail.dll and IMAP is as follows.

using Limilabs.Client.IMAP;
using Limilabs.Mail;
using Limilabs.Mail.MIME
using System;
using System.Collections.Generic;

class Program
{
    static void Main(string[] args)
    {
        using(Imap imap = new Imap())
        {
            imap.ConnectSSL("imap.example.com");
            imap.UseBestLogin("user", "password");

            imap.SelectInbox();
            List<long>; uids = imap.Search(Flag.Unseen);
            foreach (long uid in uids)
            {
                var eml = imap.GetMessageByUID(uid);
                IMail email = new MailBuilder()
                    .CreateFromEml(eml);
                Console.WriteLine(email.Subject);

                foreach (MimeData mime in email.Attachments)
                {
                    mime.Save(@"c:\" + mime.SafeFileName);
                }
            }
            imap.Close();
        }
    }
};

Below is the VB.NET code for your reference:

Imports Limilabs.Client.IMAP
Imports Limilabs.Mail
Imports Limilabs.Mail.MIME
Imports System
Imports System.Collections.Generic

Public Module Module1
    Public Sub Main(ByVal args As String())

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

            imap.SelectInbox()
            Dim uids As List(Of Long) = imap.Search(Flag.Unseen)

            For Each uid As Long In uids
                Dim eml = imap.GetMessageByUID(uid)
                Dim email As IMail = New MailBuilder() _
                    .CreateFromEml(eml)
                Console.WriteLine(email.Subject)

                For Each mime As MimeData In email.Attachments
                    mime.Save("c:\" + mime.SafeFileName)
                Next
            Next
            imap.Close()
        End Using

    End Sub
End Module

Accessing attachment data

You can also save attachment to a specific stream using MimeData.Save(Stream stream).

You can get direct access to attachment binary data with MimeData.GetMemoryStream().

Finally you can get a byte array (byte[]) using MimeData.Data property.

Downloading only parts of the message

IMAP protocol provides very useful features in regard to working with attachments and all are available in Mail.dll .NET IMAP component.

With Mail.dll you can download only parts of email message, which in conjunction with getting basic email information without downloading entire message can make your code extremely fast.

Process emails embedded as attachments

In some situations you’ll receive a message that has another message attached.

You can use Mail.dll to extract all attachments from such inner messages no matter how deep the embedding level is.

Tags: Attachments C# Email component IMAP IMAP component VB.NET