Open EML File

Understanding the RFC-822 format and its relation to EML files

The RFC 822 standard describes the format of email messages, and together with RFC 821, which describes the protocol followed by computers on the Internet to exchange mail in a robust, reliable and efficient way, they define the SMTP protocol, whose basic message transport represents the standard for exchanging messages using the TCP/IP protocol, either on the intranet or on the internet.

According to RFC 822 standard each message consists of two parts:

Envelope: which contains all the necessary information so that the message can be transmitted and delivered to the recipient.

Content: which is the information that must be delivered to the recipient, formed by lines of text. To include images or other information, a filter must be used.

Each message contains part of the information in structured format, named header, with several fields, and part in a free format, named body.

Some important fields are those that define the date of sending the message, the address of origin, the destination, references, object of the message, etc. A particular importance is the address field, which identifies each user in a unique way, which has that format that is already so familiar to us: User@domain where the domain is the official and registered name of a network or computer of the Network, which can be structured in several subdomains, and the user is the name of the person within that domain.

The main purpose of creating an .EML file is to use it for the long-term backup or storage and allow the forwarding of email messages and their content.

The format specifications of the EML files are available according to the RFC 822 standard. Before RFC 822 entered the scene, the RFC-733 standard regulated the exchange of network messages until 1982. RFC 822 was created as an improvement within the ARPA standards. At the same time, Microsoft created its own email client, named Outlook Express, creating in this way, its own e-mail infrastructure. Microsoft switched from RFC-822 to a proprietary PST file format thus separating itself from the open standard. In PST files emails are stored in a highly structured database format.

This resulted in problems for users of non-Microsoft email clients when sending emails from Microsoft Outlook. One of the problems that arose was that non-standardized Outlook emails often came as winmail.dat files that are not discernible and not readable to users of other email clients.

Due to this many applications can create emails with the .EML extension that are saved in the MIME RFC-822 format. EML files have a standard file structure and often use simple ASCII text to write the header and body of the main message. The header includes the sender's email address, the recipient's email address, the subject line text and the time and date the message was sent.

The main message is in the body of the .eml file where hyperlinks and attachments can also be embedded.