Sustainability of Digital Formats: Planning for Library of Congress Collections

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Email (Electronic Mail Format)

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Format Description Properties Explanation of format description terms

Identification and description Explanation of format description terms

Full name Email (Electronic Mail Format)

EML, short for electronic mail or email, is a file extension for an email message saved to a file in the Internet Message Format protocol for electronic mail messages. It is the standard format used by Microsoft Outlook Express as well as some other email programs. Since EML files are created to comply with industry standard RFC 5322, EML files can be used with most email clients, servers and applications. See IMF for a description of the message syntax.

EML files typically store each message as a single file (unlike MBOX which concatenates all the messages from a folder into one file), and attachments may either be included as MIME content in the message or written off as a separate file, referenced from a marker in the EML file.

Production phase Used for content in initial (by message authors), middle (by archives) or final state (by message recipients/other end users).
Relationship to other formats
    Defined via IMF, Internet Mail Format

Local use Explanation of format description terms

LC experience or existing holdings The Library of Congress includes EML files in its collections, especially in the Manuscripts and Music Divisions as well as other personal papers repositories.
LC preference The Library of Congress Recommended Formats Statement (RFS) lists EML as an acceptable format for Email: For individual messages.

Sustainability factors Explanation of format description terms

Disclosure Partially documented through RFC 5322 but documentation about EML specifically is not readily available. Comments welcome.
    Documentation There is no known specification that defines EML as a file format to store email messages on a file system although it is commonly considered to be an extension of IMF as defined in RFC 5322.

Besides the Microsoft Outlook Express, EML files can be opened using most email clients, such as Microsoft Outlook, Microsoft Entourage, Mozilla Thunderbird, Apple Mail, or IncrediMail. Since EML files are plain text and formatted much like MHT (MIME HTML) files, they can also be opened directly in the Internet Explorer, Mozilla Firefox and Opera, by first changing the file extension from .eml to .mht. It is also possible to view EML files using notepad or any other text editor.

Windows 8, however, does not natively support EML in the built in Mail application so an EML Reader was developed in order to support reading EML files.

Prom reports that MBOX and EML have "achieved a certain status as de facto standards because most modern email clients and servers can import and export one or both of the formats" including Thunderbird, Apple Mail, Outlook and Eudora. In addition, external programs such as Aid4Mail, Emailchemy and Xena can convert between the two formats and numerous proprietary formats. Once in an MBOX or EML format, the data can be parsed into XML using standardized schemas.

The ePADD project developed at Stanford University Libraries added functionality for export to EML (link via Internet Archive) as of 2023 with version 10.0. This is in addition to existing export to MBOX.

    Licensing and patents None

EML files are usually simple text files and can be opened in Notepad or a web browser, either by changing the extension from eml to txt or HTML, or by changing the file association to Notepad.

Self-documentation See IMF
External dependencies None
Technical protection considerations None

Quality and functionality factors Explanation of format description terms

File type signifiers and format identifiers Explanation of format description terms

Tag Value Note
Filename extension eml
Internet Media Type message/rfc822
This is the common MIME type for all formats based on RFC 822.
Pronom PUID See note.  No corresponding PUID because EML is based on IMF
Wikidata Title ID See note.  See IMF

Notes Explanation of format description terms


Format specifications Explanation of format description terms

Useful references


Last Updated: 08/29/2023