Technologies are described for dynamic attachment delivery in emails for advanced malicious content filtering. An email service may intercept emails with attachments (or other threats such as links, embedded objects, etc.) and detach the threat (e.g., attachment) from the email allowing the email to be forwarded to the recipient without delay. The threat may be sequestered and analyzed. If the threat is determined to be harmless, it may be reattached to the email and the client notified so they can open the attachment, activate the link, or perform comparable actions.