Hi,
I am trying to use mailpile as a replacement for RoundCube. I have several users which I manage through Directadmin.
How do I set up mailpile in a way it connects to my mailserver? Can I point mailpile to my smtp / imap server location?
Also: If I would want to allow alldomains.com/webmail to display mailpile instead of roundcube, to what public folder can I direct this symlink?
Sjoerd
Mailpile is not a replacement for RoundCube. These two apps solve different problems.
RoundCube is basically a bridge that translates IMAP into web pages. As a result it is easy to scale up to thousands of users and it drops right in to traditional hosting environments. The complexity is largely “out-sourced” to the IMAP and database servers.
Mailpile is designed a a single-user application, like Firefox or LibreOffice, meant to be run on a computer directly under the control of the user of the application. It stores a large amount of data locally and it uses a large amount of RAM per user. It includes a built-in search engine and it directly handles sensitive material, such as encrypted e-mail and encryption keys - things that most people would prefer the remote server never had access to (that is the entire point of end-to-end encryption).
Mailpile is a terrible replacement for RoundCube, and RoundCube is a terrible replacement for Mailpile. They’re just different. 
Though I wanted to, I’ll refrain from replying in Dutch.
Different design
Although I understand where you are coming from, with Mailpile’s pretty UX, it goes against the grain to use it as a webmail application/script. Mailpile is designed to reclaim the privacy of your inbox. With your idea, the email would still live on the server. I guess that is what @BjarniRunar explains.
Setup
Personally, I think that Rainloop has a pretty decent UX for webmail. And if that doesn’t fit your personal needs properly, take a look at Cypth. You could still use Mailpile/Multipile, but personally, I’d set it up on a different machine and only allow access to people you trust (and vice versa). Or even better: help the users to setup Mailpile on their own machine 
Just my two cents.