In addition to the Send to and Assign fields -- which can have any email address added to them -- there is a “Share” function that lets you share posts outside of Fieldlens.
From the web app, just click the "..." button on the top right of any post. Then click Share.
You'll be able to enter the email address of any person or company you wish to share the post with -- or copy a public link to send with email, text or anything at all.
On mobile, click into the specific post you want to share, and click the "..." on the top right. Tap Share post and choose to share via email, text message, social media and more.
Sharing takes the post out of Fieldlens. It will get sent to the people you specify, and any replies you send will go directly to you and your inbox -- rather than posting back into Fieldlens.