<div>
Exim is an MTA (SMTP).<br />
<br />
I prefer Dovecot for POP and IMAP.
</div>


Exim is an MTA (SMTP).

I prefer Dovecot for POP and IMAP.

<div>
Exim storage in Maildir or mailbox format?<br />
There are several options, what features/options are you looking for beyond the pop3?<br />
Courier-IMAP (a sub set of Courier Mailserver)
</div>


Exim storage in Maildir or mailbox format?
There are several options, what features/options are you looking for beyond the pop3?
Courier-IMAP (a sub set of Courier Mailserver)

<div>
Mailbox type is a personal preference. &nbsp;I like Maildir but use both.<br />
<br />
Maildir uses one file per message so mailbox locking to add or delete messages is not an issue.<br />
<br />
I can't speak for Courier-IMAP. &nbsp;I use and like Dovecot.
</div>


Mailbox type is a personal preference.  I like Maildir but use both.

Maildir uses one file per message so mailbox locking to add or delete messages is not an issue.

I can't speak for Courier-IMAP.  I use and like Dovecot.

<div>
<div class="content wysiwyg-content">
I have a task to urgently install POP3 service for and existing exim installation on Debian 8.<br />
Which POP3 server is the best? Please link configuration guide if possible.
</div>
</div>


I have a task to urgently install POP3 service for and existing exim installation on Debian 8.
Which POP3 server is the best? Please link configuration guide if possible.

Best POP3 for exim and configuration guide

Within Internet message handling services (MHS), a message transfer agent or mail transfer agent (MTA) or mail relay is software that transfers electronic mail messages from one computer to another using a client–server application architecture. A MTA implements both the client (sending) and server (receiving) portions of the Simple Mail Transfer Protocol (SMTP). The terms mail server, mail exchanger, and MX host may also refer to a computer performing the MTA function. The Domain Name System (DNS) associates a mail server to a domain with mail exchanger (MX) resource records containing the domain name of a host providing MTA services.

Email Servers

Linux is a UNIX-like open source operating system with hundreds of distinct distributions, including: Fedora, openSUSE, Ubuntu, Debian, Slackware, Gentoo, CentOS, and Arch Linux. Linux is generally associated with web and database servers, but has become popular in many niche industries and applications.

Linux

An email client, email reader or more formally mail user agent (MUA) is a computer program used to access and manage a user's email. A web application that provides message management, composition, and reception functions is sometimes also considered an email client, but more commonly referred to as webmail.

Email Software

Interactions between email servers and clients are governed by email protocols. The three most common email protocols are POP, IMAP and MAPI. Most email software operates under one of these (and many products support more than one).  The correct protocol must be selected, and correctly configured, if you want your email account to work.