- 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
OfflineIMAP is not the way to go. Many ISPs have very low size limits for the mailbox sizes. The one I am looking at right now does have this problem (unless you pay extra).
From what I have gathered now, your hints about Postfix and fetchmail are correct. The trouble is that those doc pages are not real-life, complete examples with Dovecot of the two possible ways: 1) multidrop/catch all, and 2) one mailbox per user.
Yes, I should be able to piece it all together. I will probably try. I just find it surprising that there is no such a complete guide yet. Because I am sure that there are a few gotchas along the way.
Yes, getmail is an alternative, and that looks like a good way too. But it's the same problem: the article is not complete. It states "how you could arrange it". It would be nice that you did not have to manually write a getmail config file per user. And an example for multidrop is missing. There is a note at the end that you should carefully plan the transport ways, but I wouldn't know yet what to do in that respect.
It's just not a guide that I can follow from top to bottom to get a first working mail server to play with. That makes it pretty hard for me at this time. I will need much more time to learn and test every little detail myself. I'm not promising anything, but I may actually invest the time if I don't find anything else more interesting in the meantime. 8-)
In any case, thanks for the hints. I know now what the way to go is. Those pesky port 25 people are not going to get me! ;-)
Regards, rdiez