Setting up Dovecot pop3 server

Dovecot is an open source IMAP and POP3 server for Linux/UNIX-like systems, written with security primarily in mind. It's fast, simple to set up, requires no special administration and it uses very little memory. We are going to setup a pop3s server. Which means it's pop3 with SSL encryption. The install will be done on OpenBSD 3.8 and use the Dovecot package from the distribution.

1. Install the dovecot binary from the OpenBSD ftp website.

pkg_add -v http://openbsd.secsup.org/3.8/packages/i386/dovecot-0.99.14p1.tgz

2. First we need to edit the /etc/ssl/dovecot-openssl.cnf file and put in the unique info you want. It does not matter what this info is because we are self-signing the cert so users will get a warning about it not being a legal cert and blah blah. Just tell them to ignore this one because you signed it. This does not mean the connection is not encrypted. Just fill in the info you want below the "[ req_dn ]". Make all of it up but put in your real severs host name in the CN line. We are making this up because we are signing the cert ourselves (not signed by a valid CA). My made up example is below.

[ req ]
default_bits = 2048
encrypt_key = no
distinguished_name = req_dn
x509_extensions = cert_type
prompt = no

[ req_dn ]
# country (2 letter code)
#C=US

# State or Province Name (full name)
#ST=AK

# Locality Name (eg. city)
#L=Here

# Organization (eg. company)
#O=Dovecot

# Organizational Unit Name (eg. section)
OU=POP3s server

# Common Name (*.example.com is also possible)
CN=mail.sever.org

# E-mail contact
[email protected]

[ cert_type ]
nsCertType = server

3.After changing the values in the file you need to run the script to actually make the certs. Run the command below and it will make and place the cert for you.

/usr/local/sbin/dovecot-mkcert.sh

4.Now that the cert is generated we need to drop in the config file below. It will only use (listen on) pop3s (port 995). It accesses the systems password file for username and password authentication. All communication is SSL encrypted. Most mail clients support pop3s now. If we use regular pop3 then all of our info is sent in cleartext and that's just plain bad. Copy the info from the config below and feel free to edit to your taste. This file is modified for the OpenBSD version of Dovecot.

## Dovecot 1.0 configuration file

# Default values are shown after each value, it's not required to uncomment
# any of the lines.

# *** NOTE *** Some values HAVE been changed for OpenBSD use.

# Base directory where to store runtime data.
base_dir = /var/dovecot/

# Protocols we want to be serving:
# imap imaps pop3 pop3s
protocols = pop3s

# IP or host address where to listen in for connections. It's not currently
# possible to specify multiple addresses. "*" listens in all IPv4 interfaces.
# "[::]" listens in all IPv6 interfaces, but may also listen in all IPv4
# interfaces depending on the operating system. You can specify ports with
# "host:port".
#imap_listen = *
#pop3_listen = *

# IP or host address where to listen in for SSL connections. Defaults
# to above non-SSL equilevants if not specified.
#imaps_listen =
pop3s_listen = *

# Disable SSL/TLS support.
ssl_disable = no

# PEM encoded X.509 SSL/TLS certificate and private key. They're opened before
# dropping root privileges, so keep the key file unreadable by anyone but
# root. Included doc/mkcert.sh can be used to easily generate self-signed
# certificate, just make sure to update the domains in dovecot-openssl.cnf
ssl_cert_file = /etc/ssl/dovecotcert.pem
ssl_key_file = /etc/ssl/private/dovecot.pem

# SSL parameter file. Master process generates this file for login processes.
# It contains Diffie Hellman and RSA parameters.
ssl_parameters_file = /var/dovecot/ssl-parameters.dat

# How often to regenerate the SSL parameters file. Generation is quite CPU
# intensive operation. The value is in hours, 0 disables regeneration
# entirely.
#ssl_parameters_regenerate = 24

# Disable LOGIN command and all other plaintext authentications unless
# SSL/TLS is used (LOGINDISABLED capability). Note that 127.*.*.* and
# IPv6 ::1 addresses are considered secure, this setting has no effect if
# you connect from those addresses.
disable_plaintext_auth = no

# Use this logfile instead of syslog(). /dev/stderr can be used if you want to
# use stderr for logging (ONLY /dev/stderr - otherwise it is closed).
#log_path =

# For informational messages, use this logfile instead of the default
#info_log_path =

# Prefix for each line written to log file. % codes are in strftime(3)
# format.
#log_timestamp = "%b %d %H:%M:%S "

##
## Login processes
##

# Directory where authentication process places authentication UNIX sockets
# which login needs to be able to connect to. The sockets are created when
# running as root, so you don't have to worry about permissions. Note that
# everything in this directory is deleted when Dovecot is started.
login_dir = /var/dovecot/login

# chroot login process to the login_dir. Only reason not to do this is if you
# wish to run the whole Dovecot without roots.
# http://wiki.dovecot.org/Rootless
#login_chroot = yes

##
## IMAP login process
##

# Executable location.
#login_executable = /usr/local/libexec/dovecot/imap-login

# User to use for the login process. Create a completely new user for this,
# and don't use it anywhere else. The user must also belong to a group where
# only it has access, it's used to control access for authentication process.
# Note that this user is NOT used to access mails.
# http://wiki.dovecot.org/UserIds
login_user = _dovecot

# Set max. process size in megabytes. If you don't use
# login_process_per_connection you might need to grow this.
#login_process_size = 32

# Should each login be processed in it's own process (yes), or should one
# login process be allowed to process multiple connections (no)? Yes is more
# secure, espcially with SSL/TLS enabled. No is faster since there's no need
# to create processes all the time.
#login_process_per_connection = yes

# Number of login processes to create. If login_process_per_user is
# yes, this is the number of extra processes waiting for users to log in.
#login_processes_count = 3

# Maximum number of extra login processes to create. The extra process count
# usually stays at login_processes_count, but when multiple users start logging
# in at the same time more extra processes are created. To prevent fork-bombing
# we check only once in a second if new processes should be created - if all
# of them are used at the time, we double their amount until limit set by this
# setting is reached. This setting is used only if login_process_per_use is yes.
#login_max_processes_count = 128

# Maximum number of connections allowed in login state. When this limit is
# reached, the oldest connections are dropped. If login_process_per_user
# is no, this is a per-process value, so the absolute maximum number of users
# logging in actually login_processes_count * max_logging_users.
#login_max_logging_users = 256

##
## POP3 login process
##

# Settings default to same as above, so you don't have to set anything
# unless you want to override them.

# Exception to above rule being the executable location.
#login_executable = /usr/local/libexec/dovecot/pop3-login

##
## Mail processes
##

# Maximum number of running mail processes. When this limit is reached,
# new users aren't allowed to log in.
#max_mail_processes = 1024

# Show more verbose process titles (in ps). Currently shows user name and
# IP address. Useful for seeing who are actually using the IMAP processes
# (eg. shared mailboxes or if same uid is used for multiple accounts).
#verbose_proctitle = no

# Show protocol level SSL errors.
#verbose_ssl = no

# Valid UID range for users, defaults to 500 and above. This is mostly
# to make sure that users can't log in as daemons or other system users.
# Note that denying root logins is hardcoded to dovecot binary and can't
# be done even if first_valid_uid is set to 0.
#first_valid_uid = 500
#last_valid_uid = 0

# Valid GID range for users, defaults to non-root/wheel. Users having
# non-valid GID as primary group ID aren't allowed to log in. If user
# belongs to supplementary groups with non-valid GIDs, those groups are
# not set.
#first_valid_gid = 1
#last_valid_gid = 0

# Grant access to these extra groups for mail processes. Typical use would be
# to give "mail" group write access to /var/mail to be able to create dotlocks.
#mail_extra_groups =

# ':' separated list of directories under which chrooting is allowed for mail
# processes (ie. /var/mail will allow chrooting to /var/mail/foo/bar too).
# This setting doesn't affect login_chroot or auth_chroot variables.
# WARNING: Never add directories here which local users can modify, that
# may lead to root exploit. Usually this should be done only if you don't
# allow shell access for users. See doc/configuration.txt for more information.
#valid_chroot_dirs =

# Default chroot directory for mail processes. This can be overridden by
# giving /./ in user's home directory (eg. /home/./user chroots into /home).
#mail_chroot =

# Default MAIL environment to use when it's not set. By leaving this empty
# dovecot tries to do some automatic detection as described in
# doc/mail-storages.txt. There's a few special variables you can use:
#
# %u - username
# %n - user part in user@domain, same as %u if there's no domain
# %d - domain part in user@domain, empty if user there's no domain
# %h - home directory
#
# You can also limit a width of string by giving the number of max. characters
# after the '%' character. For example %1u gives the first character of
# username. Some examples:
#
# default_mail_env = maildir:/var/mail/%1u/%u/Maildir
# default_mail_env = mbox:~/mail/:INBOX=/var/mail/%u
# default_mail_env = mbox:/var/mail/%d/%n/:INDEX=/var/indexes/%d/%n
#
#default_mail_env =

# Space-separated list of fields to cache for all mails. Currently these
# fields are allowed followed by a list of commands they speed up:
#
# Envelope - FETCH ENVELOPE and SEARCH FROM, TO, CC, BCC, SUBJECT,
# SENTBEFORE, SENTON, SENTSINCE, HEADER MESSAGE-ID,
# HEADER IN-REPLY-TO
# Body - FETCH BODY
# Bodystructure - FETCH BODY, BODYSTRUCTURE
# MessagePart - FETCH BODY[1.2.3] (ie. body parts), RFC822.SIZE,
# SEARCH SMALLER, LARGER, also speeds up BODY/BODYSTRUCTURE
# generation. This is always set with mbox mailboxes, and
# also default with Maildir.
#
# Different IMAP clients work in different ways, that's why Dovecot by default
# only caches MessagePart which speeds up most operations. Whenever client
# does something where caching could be used, the field is automatically marked
# to be cached later. For example after FETCH BODY the BODY will be cached
# for all new messages. Normally you should leave this alone, unless you know
# what most of your IMAP clients are. Caching more fields than needed makes
# the index files larger and generate useless I/O.
#
# With maildir there's one extra optimization - if nothing is cached, indexing
# the maildir becomes much faster since it's not opening any of the mail files.
# This could be useful if your IMAP clients access only new mails.

#mail_cache_fields = MessagePart

# Space-separated list of fields that Dovecot should never set to be cached.
# Useful if you want to save disk space at the cost of more I/O when the fields
# needed.
#mail_never_cache_fields =

# Workarounds for various client bugs:
# oe6-fetch-no-newmail:
# Never send EXISTS/RECENT when replying to FETCH command. Outlook Express
# seems to think they are FETCH replies and gives user "Message no longer
# in server" error. Note that OE6 still breaks even with this workaround
# if synchronization is set to "Headers Only".
# outlook-idle:
# Outlook and Outlook Express never abort IDLE command, so if no mail
# arrives in half a hour, Dovecot closes the connection. This is still
# fine, except Outlook doesn't connect back so you don't see if new mail
# arrives.
# outlook-pop3-no-nuls:
# Outlook and Outlook Express hang if mails contain NUL characters.
# This setting replaces them with 0x80 character.
#client_workarounds =

# Dovecot can notify client of new mail in selected mailbox soon after it's
# received. This setting specifies the minimum interval in seconds between
# new mail notifications to client - internally they may be checked more or
# less often. Setting this to 0 disables the checking.
# NOTE: Evolution client breaks with this option when it's trying to APPEND.
#mailbox_check_interval = 0

# Like mailbox_check_interval, but used for IDLE command.
#mailbox_idle_check_interval = 30

# Allow full filesystem access to clients. There's no access checks other than
# what the operating system does for the active UID/GID. It works with both
# maildir and mboxes, allowing you to prefix mailboxes names with eg. /path/
# or ~user/.
#mail_full_filesystem_access = no

# Maximum allowed length for custom flag name. It's only forced when trying
# to create new flags.
#mail_max_flag_length = 50

# Save mails with CR+LF instead of plain LF. This makes sending those mails
# take less CPU, especially with sendfile() syscall with Linux and FreeBSD.
# But it also creates a bit more disk I/O which may just make it slower.
#mail_save_crlf = no

# Use mmap() instead of read() to read mail files. read() seems to be a bit
# faster with my Linux/x86 and it's better with NFS, so that's the default.
# Note that this option doesn't work correctly on OpenBSD as msync() needs
# the MS_INVALIDATE to operate properly. Enable at your own risk.
#mail_read_mmaped = no

# By default LIST command returns all entries in maildir beginning with dot.
# Enabling this option makes Dovecot return only entries which are directories.
# This is done by stat()ing each entry, so it causes more disk I/O.
# (For systems setting struct dirent->d_type, this check is free and it's
# done always regardless of this setting)
#maildir_stat_dirs = no

# Copy mail to another folders using hard links. This is much faster than
# actually copying the file. This is problematic only if something modifies
# the mail in one folder but doesn't want it modified in the others. I don't
# know any MUA which would modify mail files directly. IMAP protocol also
# requires that the mails don't change, so it would be problematic in any case.
# If you care about performance, enable it.
#maildir_copy_with_hardlinks = no

# Call mmap() with MS_INVALIDATE flag each time before accessing message
# indexes. This option is recommended on OpenBSD 3.4 and older versions
# to negate the risk of corruption when rebuilding indexes.
# It's also required if you insist on saving index files over NFS.
index_mmap_invalidate = yes

# Check if mails' content has been changed by external programs. This slows
# down things as extra stat() needs to be called for each file. If changes are
# noticed, the message is treated as a new message, since IMAP protocol
# specifies that existing messages are immutable.
#maildir_check_content_changes = no

# Which locking methods to use for locking mbox. There's three available:
# dotlock: Create <mailbox>.lock file. This is the oldest and most NFS-safe
# solution. If you want to use /var/mail/ like directory, the users
# will need write access to that directory.
# fcntl : Use this if possible. Works with NFS too if lockd is used.
# flock : May not exist in all systems. Doesn't work with NFS.
#
# You can use both fcntl and flock too; if you do the order they're declared
# with is important to avoid deadlocks if other MTAs/MUAs are using both fcntl
# and flock. Some operating systems don't allow using both of them
# simultaneously, eg. BSDs. If dotlock is used, it's always created first.
mbox_locks = fcntl

# Should we create dotlock file even when we want only a read-lock? Setting
# this to yes hurts the performance when the mailbox is accessed simultaneously
# by multiple processes, but it's needed for reliable reading if no other
# locking methods are available.
#mbox_read_dotlock = no

# Maximum time in seconds to wait for lock (all of them) before aborting.
#mbox_lock_timeout = 300

# If dotlock exists but the mailbox isn't modified in any way, override the
# lock file after this many seconds.
#mbox_dotlock_change_timeout = 30

# umask to use for mail files and directories
#umask = 0077

# Drop all privileges before exec()ing the mail process. This is mostly
# meant for debugging, otherwise you don't get core dumps. Note that setting
# this to yes means that log file is opened as the logged in user, which
# might not work. It could also be a small security risk if you use single UID
# for multiple users, as the users could ptrace() each others processes then.
#mail_drop_priv_before_exec = no

##
## IMAP process
##

# Executable location
#imap_executable = /usr/local/libexec/dovecot/imap

# Set max. process size in megabytes. Most of the memory goes to mmap()ing
# files, so it shouldn't harm much even if this limit is set pretty high.
#imap_process_size = 256

# Support for dynamically loadable modules.
#imap_use_modules = no
#imap_modules = /usr/local/lib/dovecot/imap

##
## POP3 process
##

# Executable location
pop3_executable = /usr/local/libexec/dovecot/pop3

# Set max. process size in megabytes. Most of the memory goes to mmap()ing
# files, so it shouldn't harm much even if this limit is set pretty high.
#pop3_process_size = 256

# Support for dynamically loadable modules.
#pop3_use_modules = no
#pop3_modules = /usr/local/lib/dovecot/pop3

##
## Authentication processes
##

# An Authentication process is a child process used by Dovecot that
# handles the authentication steps. The steps cover an authentication
# mechanism (auth_mechanisms, how the client authenticates in the IMAP or
# POP3 protocol), which password database should be queried (auth_passdb),
# and which user database should be queried (auth_userdb, to obtain
# UID, GID, and location of the user's mailbox/home directory).
#
# You can have multiple processes, though a typical configuration will
# have only one. Each time "auth = xx" is seen, a new process
# definition is started. The point of multiple processes is to be able
# to set stricter permissions. (See auth_user below.)
#
# Just remember that only one Authentication process is asked for the
# password, so you can't have different passwords accessible through
# different process definitions (unless they have different
# auth_mechanisms, and you're ok with having different password for
# each mechanisms).

# Authentication process name.
auth = default

# Specifies how the client authenticates in the IMAP protocol.
# Space separated list of permitted authentication mechanisms:
# anonymous plain digest-md5 cram-md5
#
# anonymous - No authentication required.
# plain - The password is sent as plain text. All IMAP/POP3 clients
# support this, and the password can be encrypted by Dovecot to match
# any of the encryption schemes used in password databases.
# digest-md5 and cram-md5 - both encrypt the password so it is more
# secure in transit, but are not well supported by clients, and
# require that the password database use a matching encryption
# scheme (or be in plaintext).
#
# See auth.txt for more details.
#
# If you are using SSL there is less benefit to digest-md5 and
# cram-md5 as the communication is already encrypted.
auth_mechanisms = plain

# Space separated list of realms for SASL authentication mechanisms that need
# them. You can leave it empty if you don't want to support multiple realms.
# Many clients simply use the first one listed here, so keep the default realm
# first.
#auth_realms =

# Default realm/domain to use if none was specified. This is used for both
# SASL realms and appending @domain to username in plaintext logins.
#auth_default_realm =

# User database specifies where mails are located and what user/group IDs
# own them. For single-UID configuration use "static".
# http://wiki.dovecot.org/Authentication
# http://wiki.dovecot.org/VirtualUsers
# passwd: /etc/passwd or similiar, using getpwnam()
# passwd-file <path>: passwd-like file with specified location
# static uid=<uid> gid=<gid> home=<dir template>: static settings
# vpopmail: vpopmail library
# ldap <config path>: LDAP, see doc/dovecot-ldap.conf
# pgsql <config path>: a PostgreSQL database, see doc/dovecot-pgsql.conf
auth_userdb = passwd

# Password database specifies only the passwords for users.
# http://wiki.dovecot.org/Authentication
# passwd: /etc/passwd or similiar, using getpwnam()
# shadow: /etc/shadow or similiar, using getspnam()
# pam [<service> | *]: PAM authentication
# passwd-file <path>: passwd-like file with specified location
# vpopmail: vpopmail authentication
# ldap <config path>: LDAP, see doc/dovecot-ldap.conf
# pgsql <config path>: a PostgreSQL database, see doc/dovecot-pgsql.conf
auth_passdb = passwd

#auth_executable = /usr/libexec/dovecot/dovecot-auth

# Set max. process size in megabytes.
#auth_process_size = 256

# User to use for the process. This user needs access to only user and
# password databases, nothing else. Only shadow and pam authentication
# requires roots, so use something else if possible. Note that passwd
# authentication with BSDs internally accesses shadow files, which also
# requires roots. Note that this user is NOT used to access mails.
# That user is specified by auth_userdb above.
auth_user = root

# Directory where to chroot the process. Most authentication backends don't
# work if this is set, and there's no point chrooting if auth_user is root.
#auth_chroot =

# Number of authentication processes to create
#auth_count = 1

# List of allowed characters in username. If the user-given username contains
# a character not listed in here, the login automatically fails. This is just
# an extra check to make sure user can't exploit any potential quote escaping
# vulnerabilities with SQL/LDAP databases. If you want to allow all characters,
# set this value to empty.
#auth_username_chars = abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ01234567890.-_@

# Username to use for users logging in with ANONYMOUS SASL mechanism
#auth_anonymous_username = anonymous

# More verbose logging. Useful for figuring out why authentication isn't
# working.
#auth_verbose = no

# Even more verbose logging for debugging purposes. Shows for example SQL
# queries.
#auth_debug = no

# digest-md5 authentication process. It requires special MD5 passwords which
# /etc/shadow and PAM doesn't support, so we never need roots to handle it.
# Note that the passwd-file is opened before chrooting and dropping root
# privileges, so it may be 0600-root owned file.

#auth = digest_md5
#auth_mechanisms = digest-md5
#auth_realms =
#auth_userdb = passwd-file /etc/passwd.imap
#auth_passdb = passwd-file /etc/passwd.imap
#auth_user = imapauth
#auth_chroot =

# if you plan to use only passwd-file, you don't need the two auth processes,
# simply set "auth_methods = plain digest-md5"

5.You will also need to put a line in /etc/rc.local to have Dovecot start on boot. That line will be below. If you want to just test it and reboot later just execute "/usr/local/sbin/dovecot". Always test that a reboot will start your daemon.

# Start Dovecot
if [ -x /usr/local/sbin/dovecot ]; then
       echo -n ' Dovecot';        /usr/local/sbin/dovecot
fi

That is it. Don't forget to put in any pf rules to let pop3s into the machine. The dovecot config above will listen on all interfaces.

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