Sustainability of Digital Formats: Planning for Library of Congress Collections

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.

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.

Harvard University Libraries' Electronic Archiving System (EAS) normalizes email messages to EML.

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.