Attachment
An attachment is a file sent along with an email message, such as a PDF, image, or spreadsheet.
An attachment is a file sent with an email message, such as a PDF, image or spreadsheet. It travels inside the message rather than behind a link.
Where attachments fit
Attachments make sense when the recipient needs the file itself and the message is one-to-one or transactional: an invoice PDF with a receipt (see transactional email), a signed contract, or a report a customer asked for.
For campaigns and lifecycle email, a link to a hosted file is usually the better choice. The message stays small, the file can be corrected after sending, and the click can be measured. A ZIP is only worth it when several small files genuinely have to travel together.
Common mistakes
Attaching a file when a link would do. Attaching something without saying in the body what it is and why it is there. Using a filename that means nothing to the recipient: for example, invoice-2026-03.pdf is easier to find later than document.pdf.