What .eml files actually contain and how to parse them without email clients

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An .eml file is a plain-text file following MIME standards (RFC 5322 and RFC 2045), readable in any text editor without specialist software like Outlook. The format begins with headers, followed by a body that can be split into multiple parts separated by a defined boundary string, with text typically encoded as quoted-printable and attachments as base64. Developers parsing .eml files must handle edge cases such as header folding, non-ASCII encoded words per RFC 2047, and inline images referenced by content IDs. Variant formats like Apple Mail's .emlx and Outlook's .msg require separate handling, as .msg is a binary OLE compound file rather than MIME. A browser-based viewer at emltool.com has been built to open .eml, .emlx, and .msg files locally without any installation.

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