It is best practice to not send emails with an attachment in bulk due to the risk of being caught in spam filters. While your intentions behind the email and its content are good, file attachments on bulk emails could expose recipients to nasty security risks and these are treated as a threat by email providers. The file is added as a .html file instead of your original document format to protect recipients against spammers, making it far more likely you’ll find yourself caught in their spam filter.
In short, there are two alternative options available in vega where you can include a link to view a document online or download it as a PDF from within the email.
Use a browser link to display your document online
In your newsletter email document, you will need to include a link to your linked newsletter content document that can be viewed online.
To do this, click the 'Get Browser Link' from the top right-hand side menu of your linked newsletter content document. This will open the document in a new tab where you can then copy the URL.
Link a downloadable PDF file
The second option available is to include a link on your text or button where the user can download a PDF file of your newsletter. This option requires you to have your newsletter in a PDF file already and this might be preferred if you have an external provider creating your newsletter document in PDF already.