Attachment
A file — such as a PDF, image, or spreadsheet — embedded in an email message and encoded as a MIME part, separate from the message body, intended for the recipient to save or open.
An attachment is a MIME part with a Content-Disposition header set to attachment, optionally including a filename parameter. The part's content is typically encoded with Base64 so that binary data can travel through text-based mail infrastructure. The Content-Type header identifies the file type, such as application/pdf or image/png, so the recipient's mail client knows how to handle it.
Attachments are one of the most common reasons people search their email archives — locating a contract, an invoice, or a photo sent years ago. Filtering by has:attachment narrows results to messages that contain at least one attached file. Additional filters on filename or file type can narrow further, for example finding all messages with a PDF attachment from a specific sender.
Mbox Viewer decodes MIME attachments and provides previews for common file types. It also supports batch export, allowing you to extract all attachments from a set of messages to a folder in one operation — useful when recovering files from a large archive without opening each message individually.
Related terms
Multipurpose Internet Mail Extensions — the standard that defines how email messages encode non-ASCII text, HTML bodies, attachments, and other binary content within the plain-text structure of email.
A binary-to-text encoding scheme that represents arbitrary binary data using only 64 printable ASCII characters, widely used in email to safely transmit attachments and binary content.
An image embedded directly into an HTML email body using a Content-ID (cid:) reference, rather than attached as a separate downloadable file. The image data is stored as a MIME part within the same message.