When emailing attachments, you have three options:
Expiring url. You can include an expiring url for the attachment in the message body. Anyone who clicks the link within a few hours of when the email is sent will be able to view and download the file. Note that the countdown begins when the email is sent (and the link is generated), not when the recipient opens the email.
Viewer url. You can include a viewer url for the attachment in the message body. Users will need to be logged into to Airtable with an account that has access to the the attachment in the base itself (not interface only-access). This link will not expire and will be good as long as the user retains access to the base and the attachment exists. You can revoke access by removing access to the base or deleting the attachment from the base.
Email Attachment. You can include the Airtable attachment as an attachment to the email, not in the body of the message. This will include the full raw contents of the file. There is no link and the user does not need to log into Airtable to view the file.