The MailASail mail service is called Teleport Mail, and is described in more detail at the MailASail site.

To use Teleport email, first, setup your email client, on macOS or iOS, as described in the MailASail documents. Once Teleport email has been setup, configure LuckGrib to send its email requests to the Apple Mail app. That’s pretty much all there is to it.

When you receive an email back from the Offshore service, click/tap on the attachment and open it in LuckGrib.