Can I use the Email app as the frontend for my private VPS email server?

We are happy to answer your questions about the code or discuss technical ideas.

Please complete the following checklist (by adding [x]):

• [Y] I have searched open and closed issues for duplicates
• [Y] This isn't a feature request
• [Y] This is not a report about my app not working as expected

I can't find a direct answer to this question. It's license is GPL but doesn't mean it's going to work with Emails servers that are not official Proton Mail servers.

So I just need a short and simple yes or no answer.

Which apps can I use that will not be restricted if I use open source tools to connect them to? For example.

Can I use Mail app with Postfix/Sendmail/Exa?
Can I use the Drive app and connect it to a Samba/NFS/Other network file system mount?
Can I use the Calendar app and sync it with my own calendar I've made which the data is stored on a PostgreSQL instance?

I'm just a bit confused by the usage & setup not being defined to clearly in the readme, and I've lost 1 week of work because of a situation similar with Tutanota, They like to claim there open source but there open source web client only works with there proprietary servers and it's pain to back engineer.

I hope this isn't a similar repo.

Thankyou.

Start by reviewing the README and any existing documentation for the Email, Drive, and Calendar apps. Identify whether external services such as Postfix, Sendmail, Samba/NFS, or a PostgreSQL-backed calendar are supported, then clarify the supported integrations and any server or licensing restrictions in the documentation.