Understand the Structure of MSG File

Get to know about what is MSG file, its, structure, properties etc.

Learn What is MSG File?

Application Supported Microsoft Outlook
Category Encapsulated Email Messages
Organization Microsoft
MIME Type application/vnd.ms-outlook

A MSG file is a Compound File Binary File Format that comprises of streams and storages. These files also contain objects, which in turn stores properties and the collection of properties. The objects are represented by storages whereas the properties are represented by streams and reside in streams.

I. Objects

Objects in a message store are created by the email client like Outlook or the server. There are three kinds of objects that can be found in a MSG file:

  • Email object
    This object is represented by the .msg compound file. Only one kind of email object is present at the top or root level. However, there can be multiple email objects at the lower level that might be present within the other object types.
  • Recipient Object
    The storages in the Recipient Object are named as follows:
    _recip_version1.0_#00000000
    _recip_version1.0_#00000001
    _recip_version1.0_#00000002
    The subsequent objects will have the names, which will differ in the serial number after the pound sign.
  • Attachment Object
    There exist two kinds of Attachment Objects.
    1. Embedded Message Attachments
      These are the other email messages that have been attached to the message. A substorage with the name _substg1.0_3701000D is created under _attach_version1.0_#(serial number) for the attachment. The content of the _substg1.0_3701000D will be another message in the MSG file.
    2. Custom Attachments
      The custom attachments are not another message. When the substorage _substg1.0_3701000D is created the client or the server, which creates the message, stops writing. The pointer then points to the application such as Word, Excel or other applications.
II. Properties

Properties in the MSG file describe the attributes of the object such as sender email, read receipt, name of the attachments, etc. each detail is defined with the help of the properties. Their structure is similar to that of arrays and they can be of fixed or variable length. There exists a property stream namely, _properties_version1.0 stream that is present at the highest level in message and in the Recipient and Attachment object storage.

  • Fixed Length Properties
    The fixed length property type is elements like PtypInteger16 bit currency integer or PtypCurrency hat is a 64-bit currency type. They are present in the _properties_version1.0 stream. It contains three kinds of information: a tag, a set of flags, and a 8-byte field.
    1. Tag
      This element uniquely defines the properties.
    2. Set of Flags
      This set of flags show whether the property is readable or writable and whether it should be present in the .msg file or attachment.
    3. 8-Byte Field
      This is the maximum length of the fixed property and contains the value of the property.
  • Variable Length Properties
    The variable length properties store strings and binary data like PtypeString and PtypBinary.
  • Multi-Value Properties
    The multi-valued properties are of two types:
    1. Fixed Length
      The fixed length multi-value properties are arrays, which have limited elements of a fixed size type.
    2. Variable Length
      The variable properties are the arrays, which have limited elements and have the same elements as of variable length properties.
The Final Words

The complete detailed structure of MSG File will help in having the complete understanding of MSG files. If you still have some doubts then, feel free to contact us our experts will look over the same.