To get attachments from Mailparser, you need to create a new parsing rule in the account which returns the meta data of the attachments. This gives the Zap the URL to where the attachment is located on their server which you can then find on the Zap!
Mailparser has default webhook behavior to send multiple webhooks if the parsed email contains results with multiple items (line items, for example). This can trigger the Zap multiple times of one parsed email. For example, this email would trigger the Zap three times:
You can turn this behavior off in Mailparser, so that it only sends one webhook per parsed email. This is a helpful link on Mailparser's site with more information about this: https://support.mailparser.io/article/226-why-are-my-webhooks-firing-multiple-times