EML file format stores a single email message inside a plain text file and was developed with RFC-822 Internet Message Format Standard. EML file consists of email headers, email body, and attachment. Many email clients support opening EML files like Windows Live Mail, Outlook Express, Thunderbird, eM Client, etc.
EML file specifications are described as per RFC 822 format. Before this, RFC-733 governed the rules of network messages exchange. Microsoft also created its own email client i.e. Outlook Express, creating its e-mail infrastructure in this way. Microsoft switched to RFC-822 to a proprietary PST file format this separating itself from the open standard.
This arises problems for non-Microsoft email clients when sending emails from Outlook. The main problem was that non-standardized Outlook emails came as winmail.dat files that are not readable by users of other email clients.
Due to this, many applications can create emails with .eml extension that are saved in MIME RFC-822 format.
Specifications of EML file
The main components of EML file are –
EML File Header – the part of email where email addresses, subject, time stamps, and encoding marks are located.
The header information includes sender email address, recipient email address, subject of email, time & date stamp of message.
EML Email Body – This is the part of the email where the main message body is stored. The email body contains links and images.
It actually represents the nature and format of the document. The structure of MIME Type or content-type is simple. It contains a type and sub-type, two strings, separated by a’/’, no space should be there. The Type specifies category and subtype specifies each type.
Some Important content-types are as follows;
| Type | Description | Example of Subtypes |
|---|---|---|
| Text | Specifies format that is readable by users | Text/plain, text/html, text/css, text/javascript |
| Image | Describes image of any type | image/bmp, image/png, image/jpg, image/gif |
| Audio | Describes audio file format | audio/mdi, audio/wav |
| Application | Specifies any kind of binary data | application/octet-stream, application/vnd.mspowerpoint, application/xhtml+xml, application/xml, application/pdf |
EML attachments – This part contains encoded attachments, placed one by one. Attachments in the message body are identified by its Content-Type and Content-Disposition. Example –.
Content-Type: text/plain; charset#“windows-1252”; name#“apple app store.txt” Content-Disposition: attachment; filename#“apple app store.txt” Content-Transfer-Encoding: base64 X-Attachment-Id: f_jkhztmd02