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/etc/courier/imapd is in courier-imap 4.17.2+0.76.3-5+deb9u1.

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##VERSION: $Id: 106596a150c4585c41d65f60a17e173402125332-20150610063509$
#
# imapd created from imapd.dist by sysconftool
#
# Do not alter lines that begin with ##, they are used when upgrading
# this configuration.
#
#  Copyright 1998 - 2015 Double Precision, Inc.  See COPYING for
#  distribution information.
#
#  This configuration file sets various options for the Courier-IMAP server
#  when used with the couriertcpd server.
#  A lot of the stuff here is documented in the manual page for couriertcpd.
#
#  NOTE - do not use \ to split long variable contents on multiple lines.
#  This will break the default imapd.rc script, which parses this file.
#
##NAME: ADDRESS:0
#
#  Address to listen on, can be set to a single IP address.
#
# ADDRESS=127.0.0.1

ADDRESS=0

##NAME: PORT:1
#
#  Port numbers that connections are accepted on.  The default is 143,
#  the standard IMAP port.
#
#  Multiple port numbers can be separated by commas.  When multiple port
#  numbers are used it is possible to select a specific IP address for a
#  given port as "ip.port".  For example, "127.0.0.1.900,192.68.0.1.900"
#  accepts connections on port 900 on IP addresses 127.0.0.1 and 192.68.0.1
#  The previous ADDRESS setting is a default for ports that do not have
#  a specified IP address.

PORT=143

##NAME: AUTHSERVICE:0
#
#  It's possible to authenticate using a different 'service' parameter
#  depending on the connection's port.  This only works with authentication
#  modules that use the 'service' parameter, such as PAM.  Example:
#
#  AUTHSERVICE143=imap
#  AUTHSERVICE993=imaps

##NAME: MAXDAEMONS:0
#
#  Maximum number of IMAP servers started
#

MAXDAEMONS=40

##NAME: MAXPERIP:0
#
#  Maximum number of connections to accept from the same IP address

MAXPERIP=20

##NAME: PIDFILE:0
#
#  File where couriertcpd will save its process ID
#

PIDFILE=/run/courier/imapd.pid

##NAME: TCPDOPTS:0
#
# Miscellaneous couriertcpd options that shouldn't be changed.
#

TCPDOPTS="-nodnslookup -noidentlookup"

##NAME: ACCESSFILE:0
#
# IMAP access file.

IMAPACCESSFILE=/etc/courier/imapaccess

##NAME: LOGGEROPTS:0
#
# courierlogger(1) options.
#

LOGGEROPTS="-name=imapd"

##NAME: DEFDOMAIN:0
#
# Optional default domain. If the username does not contain the
# first character of DEFDOMAIN, then it is appended to the username.
# If DEFDOMAIN and DOMAINSEP are both set, then DEFDOMAIN is appended
# only if the username does not contain any character from DOMAINSEP.
# You can set different default domains based on the the interface IP
# address using the -access and -accesslocal options of couriertcpd(1).

#DEFDOMAIN="@example.com"

##NAME: IMAP_CAPABILITY:1
#
# IMAP_CAPABILITY specifies what most of the response should be to the
# CAPABILITY command.
#
# If you have properly configured Courier to use CRAM-MD5, CRAM-SHA1, or
# CRAM-SHA256 authentication (see INSTALL), set IMAP_CAPABILITY as follows:
#
# IMAP_CAPABILITY="IMAP4rev1 UIDPLUS CHILDREN NAMESPACE THREAD=ORDEREDSUBJECT THREAD=REFERENCES SORT QUOTA AUTH=CRAM-MD5 AUTH=CRAM-SHA1 AUTH=CRAM-SHA256 IDLE"
#

IMAP_CAPABILITY="IMAP4rev1 UIDPLUS CHILDREN NAMESPACE THREAD=ORDEREDSUBJECT THREAD=REFERENCES SORT QUOTA IDLE"

##NAME: KEYWORDS_CAPABILITY:0
#
# IMAP_KEYWORDS=1 enables custom IMAP keywords.  Set this option to 0 to
# disable custom keywords.
#
# IMAP_KEYWORDS=2 also enables custom IMAP keywords, but uses a slower
# algorithm. Use this setting if keyword-related problems occur when
# multiple IMAP clients are updating keywords on the same message.

IMAP_KEYWORDS=1

##NAME: ACL_CAPABILITY:0
#
# IMAP_ACL=1 enables IMAP ACL extension. Set this option to 0 to
# disable ACL capabilities announce.

IMAP_ACL=1

##NAME: SMAP1_CAPABILITY:0
#
# EXPERIMENTAL
#
# To enable the experimental "Simple Mail Access Protocol" extensions,
# uncomment the following setting.
#
# SMAP_CAPABILITY=SMAP1

##NAME: IMAP_CAPABILITY_ORIG:2
#
# For use by webadmin

IMAP_CAPABILITY_ORIG="IMAP4rev1 UIDPLUS CHILDREN NAMESPACE THREAD=ORDEREDSUBJECT THREAD=REFERENCES SORT QUOTA AUTH=CRAM-MD5 AUTH=CRAM-SHA1 AUTH=CRAM-SHA256 IDLE"

##NAME: IMAP_PROXY:0
#
# Enable proxying.  See README.proxy

IMAP_PROXY=0

##NAME: PROXY_HOSTNAME:0
#
# Override value from gethostname() when checking if a proxy connection is
# required.
#
# PROXY_HOSTNAME=

##NAME: IMAP_PROXY_FOREIGN:0
#
# Proxying to non-Courier servers.  Re-sends the CAPABILITY command after
# logging in to the remote server.  May not work with all IMAP clients.

IMAP_PROXY_FOREIGN=0

##NAME: IMAP_IDLE_TIMEOUT:0
#
# This setting controls how often
# the server polls for changes to the folder, in IDLE mode (in seconds).

IMAP_IDLE_TIMEOUT=60

##NAME: IMAP_MAILBOX_SANITY_CHECK:0
#
# Sanity check -- make sure home directory and maildir's ownership matches
# the IMAP server's effective uid and gid

IMAP_MAILBOX_SANITY_CHECK=1

##NAME: IMAP_CAPABILITY_TLS:0
#
# The following setting will advertise SASL PLAIN authentication after
# STARTTLS is established.  If you want to allow SASL PLAIN authentication
# with or without TLS then just comment this out, and add AUTH=PLAIN to
# IMAP_CAPABILITY

IMAP_CAPABILITY_TLS="$IMAP_CAPABILITY AUTH=PLAIN"

##NAME: IMAP_TLS_ORIG:0
#
# For use by webadmin

IMAP_CAPABILITY_TLS_ORIG="$IMAP_CAPABILITY_ORIG AUTH=PLAIN"

##NAME: IMAP_DISABLETHREADSORT:0
#
# Set IMAP_DISABLETHREADSORT to disable the THREAD and SORT commands -
# server side sorting and threading.
#
# Those capabilities will still be advertised, but the server will reject
# them.  Set this option if you want to disable all the extra load from
# server-side threading and sorting.  Not advertising those capabilities
# will simply result in the clients reading the entire folder, and sorting
# it on the client side.  That will still put some load on the server.
# advertising these capabilities, but rejecting the commands, will stop this
# silliness.
#

IMAP_DISABLETHREADSORT=0

##NAME: IMAP_CHECK_ALL_FOLDERS:0
#
# Set IMAP_CHECK_ALL_FOLDERS to 1 if you want the server to check for new
# mail in every folder.  Not all IMAP clients use the IMAP's new mail
# indicator, but some do.  Normally new mail is checked only in INBOX,
# because it is a comparatively time consuming operation, and it would be
# a complete waste of time unless mail filters are used to deliver
# mail directly to folders.
#
# When IMAP clients are used which support new mail indication, and when
# mail filters are used to sort incoming mail into folders, setting
# IMAP_CHECK_ALL_FOLDERS to 1 will allow IMAP clients to announce new
# mail in folders.  Note that this will result in slightly more load on the
# server.
#

IMAP_CHECK_ALL_FOLDERS=0

##NAME: IMAP_OBSOLETE_CLIENT:0
#
# Set IMAP_OBSOLETE_CLIENT if your IMAP client expects \\NoInferiors to mean
# what \\HasNoChildren really means.

IMAP_OBSOLETE_CLIENT=0

##NAME: IMAP_UMASK:0
#
# IMAP_UMASK sets the umask of the server process.  The value of IMAP_UMASK is
# simply passed to the "umask" command.  The default value is 022.
#
# This feature is mostly useful for shared folders, where the file permissions
# of the messages may be important.

IMAP_UMASK=022

##NAME: IMAP_ULIMITD:0
#
# IMAP_ULIMITD sets the maximum size of the data segment of the server
# process.  The value of IMAP_ULIMITD is simply passed to the "ulimit -d"
# command (or ulimit -v).  The argument to ulimi sets the upper limit on the
# size of the data segment of the server process, in kilobytes.  The default
# value of 65536 sets a very generous limit of 64 megabytes, which should
# be more than plenty for anyone.
#
# This feature is used as an additional safety check that should stop
# any potential denial-of-service attacks that exploit any kind of
# a memory leak to exhaust all the available memory on the server.
# It is theoretically possible that obscenely huge folders will also
# result in the server running out of memory when doing server-side
# sorting (by my calculations you have to have at least 100,000 messages
# in a single folder, for that to happen).

IMAP_ULIMITD=131072

##NAME: IMAP_USELOCKS:0
#
# Setting IMAP_USELOCKS to 1 will use dot-locking to support concurrent
# multiple access to the same folder.  This incurs slight additional
# overhead.  Concurrent multiple access will still work without this setting,
# however occasionally a minor race condition may result in an IMAP client
# downloading the same message twice, or a keyword update will fail.
#
# IMAP_USELOCKS=1 is strongly recommended when shared folders are used.

IMAP_USELOCKS=1

##NAME: IMAP_SHAREDINDEXFILE:0
#
# The index of all accessible folders.  Do not change this setting unless
# you know what you're doing.  See README.sharedfolders for additional
# information.

IMAP_SHAREDINDEXFILE=/etc/courier/shared/index

##NAME: IMAP_ENHANCEDIDLE:0
#
# If Courier was compiled with the File Alteration Monitor, setting
# IMAP_ENHANCEDIDLE to 1 enables enhanced IDLE mode, where multiple
# clients may open the same folder concurrently, and receive updates to
# folder contents in realtime.  See the imapd(8) man page for additional
# information.
#
# IMPORTANT: IMAP_USELOCKS *MUST* also be set to 1, and IDLE must be included
# in the IMAP_CAPABILITY list.
#

IMAP_ENHANCEDIDLE=0

##NAME: IMAP_TRASHFOLDERNAME:0
#
# The name of the magic trash Folder.  For MSOE compatibility,
# you can set IMAP_TRASHFOLDERNAME="Deleted Items".
#
# IMPORTANT:  If you change this, you must also change IMAP_EMPTYTRASH

IMAP_TRASHFOLDERNAME=Trash

##NAME: IMAP_EMPTYTRASH:0
#
# The following setting is optional, and causes messages from the given
# folder to be automatically deleted after the given number of days.
# IMAP_EMPTYTRASH is a comma-separated list of folder:days.  The default
# setting, below, purges 7 day old messages from the Trash folder.
# Another useful setting would be:
#
# IMAP_EMPTYTRASH=Trash:7,Sent:30
#
# This would also delete messages from the Sent folder (presumably copies
# of sent mail) after 30 days.  This is a global setting that is applied to
# every mail account, and is probably useful in a controlled, corporate
# environment.
#
# Important: the purging is controlled by CTIME, not MTIME (the file time
# as shown by ls).  It is perfectly ordinary to see stuff in Trash that's
# a year old.  That's the file modification time, MTIME, that's displayed.
# This is generally when the message was originally delivered to this
# mailbox.  Purging is controlled by a different timestamp, CTIME, which is
# changed when the file is moved to the Trash folder (and at other times too).
#
# You might want to disable this setting in certain situations - it results
# in a stat() of every file in each folder, at login and logout.
#

IMAP_EMPTYTRASH=Trash:7

##NAME: IMAP_MOVE_EXPUNGE_TO_TRASH:0
#
# Set IMAP_MOVE_EXPUNGE_TO_TRASH to move expunged messages to Trash.  This
# effectively allows an undo of message deletion by fishing the deleted
# mail from trash.  Trash can be manually expunged as usually, and mail
# will get automatically expunged from Trash according to IMAP_EMPTYTRASH.
#
# NOTE: shared folders are still expunged as usual.  Shared folders are
# not affected.
#

IMAP_MOVE_EXPUNGE_TO_TRASH=0

##NAME: IMAP_LOG_DELETIONS:0
#
#
# Set IMAP_LOG_DELETIONS to log all message deletions to syslog.
#
# IMAP_LOG_DELETIONS=1

##NAME: AUTH_MKHOMEDIR_SKEL:0
#
# Uncomment this setting to automatically create a home directory on first
# login. if the AUTH_MKHOMEDIR_SKEL environment variable is set, and the
# home directory does not exist, the home directory gets created, with its
# initial contents copied from AUTH_MKHOMEDIR_SKEL which must be a directory,
# typically /etc/skel.
#
# Note that this must be a complete home directory structure, including
# the maildir. Typically:
#
# mkdir /etc/skel
# chmod 700 /etc/skel
# maildirmak /etc/skel/Maildir
#
# This directory gets copied as is, preserving each file/subdirectory's
# permissions, with only userid/groupid changed to match the account's.
#
#
# AUTH_MKHOMEDIR_SKEL=/etc/skel

##NAME: IMAPDEBUGFILE:0
#
# IMAPDEBUGFILE="imaplog.dat"
#
# Generate diagnostic logging of IMAP commands.
#
# Set this globally, restart the server. Touch this file in an account's
# maildir directory, and Courier-IMAP will append all IMAP commands received
# for new sessions for this account. NOTE: existing IMAP sessions are not
# affected, only new IMAP logins.


##NAME: OUTBOX:0
#
# The next set of options deal with the "Outbox" enhancement.
# Uncomment the following setting to create a special folder, named
# INBOX.Outbox
#
# OUTBOX=.Outbox

##NAME: SENDMAIL:0
#
# If OUTBOX is defined, mail can be sent via the IMAP connection by copying
# a message to the INBOX.Outbox folder.  For all practical matters,
# INBOX.Outbox looks and behaves just like any other IMAP folder.  If this
# folder doesn't exist it must be created by the IMAP mail client, just
# like any other IMAP folder.  The kicker: any message copied or moved to
# this folder is will be E-mailed by the Courier-IMAP server, by running
# the SENDMAIL program.  Therefore, messages copied or moved to this
# folder must be well-formed RFC-2822 messages, with the recipient list
# specified in the To:, Cc:, and Bcc: headers.  Courier-IMAP relies on
# SENDMAIL to read the recipient list from these headers (and delete the Bcc:
# header) by running the command "$SENDMAIL -oi -t -f $SENDER", with the
# message piped on standard input.  $SENDER will be the return address
# of the message, which is set by the authentication module.
#
# DO NOT MODIFY SENDMAIL, below, unless you know what you're doing.
#

SENDMAIL=/usr/sbin/sendmail

##NAME: HEADERFROM:0
#
# For administrative and oversight purposes, the return address, $SENDER
# will also be saved in the X-IMAP-Sender mail header.  This header gets
# added to the sent E-mail (but it doesn't get saved in the copy of the
# message that's saved in the folder)
#
# WARNING - By enabling OUTBOX above, *every* IMAP mail client will receive
# the magic OUTBOX treatment.  Therefore advance LARTing is in order for
# _all_ of your lusers, until every one of them is aware of this.  Otherwise if
# OUTBOX is left at its default setting - a folder name that might be used
# accidentally - some people may be in for a rude surprise.  You can redefine
# the name of the magic folder by changing OUTBOX, above.  You should do that
# and pick a less-obvious name.  Perhaps brand it with your organizational
# name ( OUTBOX=.WidgetsAndSonsOutbox )

HEADERFROM=X-IMAP-Sender

##NAME: ID_FIELDS:0
#
# Have the server be polite, and identify its version to the client. The client
# must be logged in before the server will identify itself. Additionally,
# the client will mutually supply its own software version, and the server will
# log it.
#
# Although the server's banner message identifies itself, in free-form manner,
# this the ID IMAP extension, for clients to log.
#
# IMAP_ID_FIELDS is the sum of the following values:
#
# 1 - identify the version of the IMAP server
# 2 - identify the operating system (if available)
# 4 - identify the operating system release (if available)
#
# A value of 0 identifies the server software only.
#
# Uncomment this setting to enable the IMAP ID extension. One reason you might
# want to enable it is to log the clients' software version. Enabling this
# setting will mutually log the client's software, in the system logs.
#
# IMAP_ID_FIELDS=0

##NAME: OUTBOX_MULTIPLE_SEND:0
#
# Remove the following comment to allow a COPY of more than one message to
# the Outbox, at a time.
#
# OUTBOX_MULTIPLE_SEND=1

##NAME: IMAPDSTART:0
#
# IMAPDSTART is not used directly.  Rather, this is a convenient flag to
# be read by your system startup script in /etc/rc.d, like this:
#
#  . /etc/courier/imapd
#
#  case x$IMAPDSTART in
#  x[yY]*)
#        /usr/lib/courier/imapd.rc start
#        ;;
#  esac
#
# The default setting is going to be NO, so you'll have to manually flip
# it to yes.

IMAPDSTART=YES

##NAME: MAILDIRPATH:0
#
# MAILDIRPATH - directory name of the maildir directory.
#
MAILDIRPATH=Maildir