I would like to start by saying that I have not seen any other forums or posts that clearly explain this thing. If there are, my poor English skills probably didn't make me understand the solution clear.
As you already understood, I am trying to set up an internal email server to download mail from some providers. Looking for the best software combinations, I came across the Postfix (MTA) and Dovecot (MDA) combination several times. And so far no problem, until I noticed that many user were using a third software which can be Getmail or Fatchmail. I don't understand at all why they use a combination of these 3 when Dovecot is already doing the MDA task. Why should I also include Fetchmail or Getmail? Should I do this to use both pop and IMAP or does it depend on how I want to download or access mail from the client?
I apologize if my English is difficult to understand and thanks in advance for your attention