Looking for a guide to collect all e-mail from the ISP mail server

[Gregory Heytings]

>
> First of all, I want to learn how to do it, just for fun.
>

If you want to do this yourself for fun, here is what I believe a good way 
to do it:

1. install and configure Dovecot with one account for each user; see for 
example https://doc.dovecot.org/configuration_manual/quick_configuration/

2. install and configure OfflineIMAP to synchronize the IMAP folders 
between your ISP IMAP server and your Dovecot server; see for example 
http://www.offlineimap.org/doc/quick_start.html

At this point you should have a functional IMAP server, and your users can 
use your ISP SMTP server to send their mails.

If you want to go one step further, and want your users to send their 
mails through your server, install and configure Postfix; see for example 
http://www.postfix.org/SOHO_README.html or 
https://www.howtoforge.com/how-to-relay-email-on-a-postfix-server

If you want to go another step further, and want to remove the mails from 
your ISP IMAP server (instead of just mirroring it in Dovecot), install 
and configure Fetchmail; see for example 
https://www.linode.com/docs/guides/using-fetchmail-to-retrieve-email/