Add a manpage and improve documentation.

4 files changed, 311 insertions, 38 deletions

diff --git a/imapsync b/imapsync
index 0aa7a41..00beec7 100755
--- a/imapsync
+++ b/imapsync
@@ -1,7 +1,7 @@
 #!/usr/bin/perl -T
 
 #----------------------------------------------------------------------
-# A minimal IMAP4 client for QRESYNC-capable servers
+# IMAP-to-IMAP synchronization program for QRESYNC-capable servers
 # Copyright © 2015 Guilhem Moulin <guilhem@fripost.org>
 #
 # This program is free software: you can redistribute it and/or modify
@@ -1059,10 +1059,6 @@ while (defined (my $row = $STH_GET_CACHE->fetchrow_hashref())) {
 
 while (@REPAIR) {
     $MAILBOX = shift @REPAIR;
-    unless (defined $MAILBOX) {
-        cleanup();
-        exit 0;
-    }
 
     $STH_GET_INDEX->execute($MAILBOX);
     ($IDX) = $STH_GET_INDEX->fetchrow_array();
@@ -1072,6 +1068,10 @@ while (@REPAIR) {
     $rIMAP->select($MAILBOX);
     repair($IDX, $MAILBOX);
 }
+if ($CONFIG{repair}) {
+    cleanup();
+    exit 0;
+}
 
 
 while(1) {
diff --git a/imapsync.1 b/imapsync.1
new file mode 100644
index 0000000..eda493a
--- /dev/null
+++ b/imapsync.1
@@ -0,0 +1,273 @@
+.TH IMAPSYNC "1" "JULY 2015" "imapsync" "User Commands"
+
+.SH NAME
+imapsync \- IMAP-to-IMAP synchronization program for QRESYNC-capable servers
+
+.SH SYNOPSIS
+.B imapsync\fR [\fIOPTION\fR ...] [\fIMAILBOX\fR ...]
+
+
+.SH DESCRIPTION
+.PP
+.B imapsync\fR performs stateful synchronization between two IMAP4rev1
+servers, then (unless the flag \fB\-\-oneshot\fR is set) keeps both
+connection open and wait for new changes to arrive.
+Such synchronization is made possible by the QRESYNC extension from
+[RFC7162]; for convenience reasons support for LIST\-EXTENDED [RFC5258],
+LIST\-STATUS [RFC5819] and UIDPLUS [RFC4315] is also required.
+Furthermore, support for LITERAL+ [RFC2088] and MULTIAPPEND [RFC3502]
+is recommended: while they are not needed for \fBimapsync\fR to work,
+these extensions greatly improve performance by reducing the number of
+required round trips.
+
+.PP
+Stateful synchronization is only possible for mailboxes supporting
+persistent message Unique Identifiers (UID) and persistent storage of
+mod\-sequences (MODSEQ); any non\-compliant mailbox will cause
+\fBimapsync\fR to abort.
+Furthermore, because UIDs are allocated not by the client but by the
+server, \fBimapsync\fR needs to keep track of associations between local
+and remote UIDs for each mailbox.
+The synchronization state of a mailbox consists of its UIDNEXT and
+HIGHESTMODSEQ values on each server;
+it is then assumed that each message with UID < $UIDNEXT have been
+replicated to the other server, and that the metadata (such as flags) of
+each message with MODSEQ <= $HIGHESTMODSEQ have been synchronized.
+Conceptually, the synchronization algorithm is derived from [RFC4549]
+with the [RFC7162, section 6.1] amendments, and works as follows:
+
+.nr step 1 1
+.IP \n[step]. 8
+SELECT (on both servers) a mailbox the current UIDNEXT or HIGHESTMODSEQ
+values of which differ from the values found in the database (for either
+server).  Use the QRESYNC SELECT parameter from [RFC7162] to list
+changes (vanished messages and flag updates) since $HIGHESTMODSEQ to
+messages with UID<$UIDNEXT.
+
+.IP \n+[step].
+Propagate these changes onto the other server: get the corresponding
+UIDs from the database, then a/ issue an UID STORE + UID EXPUNGE command
+to remove messages that have not already been deleted on both servers,
+and /b issue UID STORE commands to propagate flag updates (send a single
+command for each flag list in order the reduce the number of round
+trips).
+(Conflicts may occur if the metadata of a message has been updated on
+both servers with different flag lists; in that case \fBimapsync\fR
+issues a warning and updates the message on each server with the union
+of both flag lists.)
+Repeat this step if the server sent some updates in the meantime.
+Otherwise, update the HIGHESTMODSEQ values in the database.
+
+.IP \n+[step].
+Process new messages (if the current UIDNEXT value differ from the one
+found in the database) by issuing an UID FETCH command and for each
+message RFC822 body received, issue an APPEND command to the other
+server on\-the\-fly.
+Repeat this step if the server received new messages in the meantime.
+Otherwise, update the UIDNEXT values in the database.
+Go back to step 2 if the server sent some updates in the meantime.
+
+.IP \n+[step].
+Go back to step 1 to proceed with the next unsynchronized mailbox.
+
+.PP
+By default \fBimapsync\fR synchronizes each subscribed mailbox;
+providing extra arguments limits the synchronization to the given
+\fIMAILBOX\fRes only.
+
+.PP
+In its default mode (unless the flag \fB\-\-oneshot\fR or
+\fB\-\-repair\fR is set), \fBimapsync\fR does not exit once all
+mailboxes have been synchronized.  Instead, it keeps both connection
+open and uses the NOTIFY command from [RFC5465] to be notified of new
+changes (on any mailbox) as soon as they arrive.  If no update is sent
+in 15 minutes, a NOOP command is issued in order not to trigger the
+servers' inactivity timeout and be logged out.
+
+.PP
+If the synchronization was interrupted during a previous run while some
+messages were being replicated (but before the UIDNEXT or HIGHESTMODSEQ
+values have been updated), \fBimapsync\fR performs a \(lqfull
+synchronization\(rq on theses messages only:
+downloading the whole UID and flag lists on each servers allows
+\fBimapsync\fR to detect messages that have been removed or for which
+their flags have changed in the meantime.
+Finally, after propagating the offline changes for these messages,
+\fBimapsync\fR resumes the synchronization for the rest of the mailbox.
+
+.SH OPTIONS
+.TP
+.B \-\-config=\fR\fIFILE\fR
+Specify an alternate configuration file.  Relative paths start from
+\fI$XDG_CONFIG_HOME\fR, or \fI~/.config\fR if the XDG_CONFIG_HOME
+environment variable is unset.
+
+.TP
+.B \-1\fR, \fB\-\-oneshot\fR
+Exit as soon as all mailboxes are synchronized, instead of passively
+waiting for updates from the open connections.
+Using \fB\-\-oneshot\fR removes the requirement that IMAP servers must
+advertise support the NOTIFY extension [RFC5465].
+
+.TP
+.B \-\-repair
+List the database anomalies and try to repair them.
+This is done by performing a so\-called \(lqfull synchronization\(rq,
+namely 1/ download all UIDs along with their flags from both the local
+and remote servers, 2/ ensure that each entry in the database corresponds
+to an existing UID, and 3/ ensure that both flag lists match.
+Any message found on a server but not in the database is replicated on
+the other server (which in the worst case, might lead to a message
+duplicate).
+Flag conflicts are solved by updating each message to the union of both
+lists.
+
+.TP
+.B \-q\fR, \fB\-\-quiet\fR
+Try to be quiet.
+
+.TP
+.B \-\-debug
+Turn on debug mode.
+Note that all IMAP traffic (excluding literals) is then printed to the
+error output.  Depending on the chosen authentication mechanism,
+this might include authentication credentials.
+
+.TP
+.B \-h\fR, \fB\-\-help\fR
+Output a brief help and exit.
+
+.TP
+.B \-\-version
+Show the version number and exit.
+
+.SH CONFIGURATION FILE
+
+Unless told otherwise by the \fB\-\-config=\fR\fIFILE\fR option,
+\fBimapsync\fR reads its configuration from
+\fI$XDG_CONFIG_HOME/imapsync\fR (or \fI~/.config/imapsync\fR if the
+XDG_CONFIG_HOME environment variable is unset) as an INI file.
+The syntax of the configuration file is a serie of
+\fIOPTION\fR=\fIVALUE\fR lines organized under some \fI[SECTION]\fR;
+lines starting with a \(oq#\(cq or \(oq;\(cq character are ignored as
+comments.
+The sections \(lq[local]\(rq and \(lq[remote]\(rq define the two IMAP
+servers to synchronize.
+Valid options are:
+
+.TP
+.I database
+SQLite version 3 database file to use to keep track of associations
+between local and remote UIDs, as well as the UIDVALIDITY, UIDNEXT and
+HIGHESTMODSEQ of each known mailbox on both servers.
+Relative paths start from \fI$XDG_DATA_HOME/imapsync\fR, or
+\fI~/.local/share/imapsync\fR if the XDG_DATA_HOME environment variable
+is unset.
+This option is only available in the default section.
+(Default: \(lq\fIhost\fR.db\)\(rq, where \fIhost\fR is taken from the
+\(lq[remote]\(rq or \(lq[local]\(rq sections, in that order.
+
+.TP
+.I type
+One of \(lqimap\(rq, \(lqimaps\(rq or \(lqtunnel\(rq.
+\fItype\fR=imap and \fItype\fR=imaps are respectively used for IMAP and
+IMAP over SSL/TLS connections over a INET socket.
+\fItype\fR=tunnel causes \fBimapsync\fR to open a pipe to a
+\fIcommand\fR instead of a raw socket.
+(Default: \(lqimaps\(rq.)
+
+.TP
+.I host
+Server hostname, for \fItype\fR=imap and \fItype\fR=imaps.
+(Default: \(lqlocalhost\(rq.)
+
+.TP
+.I port
+Server port.
+(Default: \(lq143\(rq for \fItype\fR=imap, \(lq993\(rq for
+\fItype\fR=imaps.)
+
+.TP
+.I command
+Command to use for \fItype\fR=tunnel.  Must speak the IMAP4rev1 protocol
+on its standard output, and understand it on its standard input.
+
+.TP
+.I STARTTLS
+Whether to use the \(lqSTARTTLS\(rq directive to upgrade a secure
+connection.  Setting this to \(lqYES\(rq for a server not advertising
+the \(lqSTARTTLS\(rq capability causes \fBimapsync\fR to immediately
+abort the connection.
+(Ignored for \fItype\fRs other than \(lqimap\(rq.  Default: \(lqYES\(rq.)
+
+.TP
+.I auth
+Space\-separated list of preferred authentication mechanisms.
+\fBimapsync\fR uses the first mechanism in that list that is also
+advertised (prefixed with \(lqAUTH=\(rq) in the server's capability list.
+Supported authentication mechanisms are \(lqPLAIN\(rq and \(lqLOGIN\(rq.
+(Default: \(lqPLAIN LOGIN\(rq.)
+
+.TP
+.I username\fR, \fIpassword\fR
+Username and password to authenticate with.  Can be required for non
+pre\-authenticated connections, depending on the chosen authentication
+mechanism.
+
+.TP
+.I SSL_cipher_list
+Cipher list to use for the connection.
+See \fIciphers\fR(1ssl) for the format of such list.
+
+.TP
+.I SSL_fingerprint
+Fingerprint of the server certificate in the form
+\fIALGO\fR$\fIDIGEST_HEX\fR, where \fIALGO\fR is the used algorithm
+(default \(lqsha256\(rq).
+Attempting to connect to a server with a non-matching certificate
+fingerprint causes \fBimapsync\fR to abort the connection immediately
+after the SSL/TLS handshake.
+
+.TP
+.I SSL_verify_trusted_peer
+Whether to verify that the peer certificate has been signed by a trusted
+Certificate Authority.  Note that using \fISSL_fingerprint\fR to specify
+the fingerprint of the server certificate is orthogonal and does not
+rely on Certificate Authorities.
+(Default: \(lqYES\(rq.)
+
+.TP
+.I SSL_ca_path
+Directory containing the certificate(s) of the trusted Certificate
+Authorities, used for server certificate verification.
+
+.SH KNOWN BUGS AND LIMITATIONS
+
+.IP \[bu] 2
+Mailbox deletion and renaming are not very well tested yet.
+.IP \[bu]
+Detecting whether a mailbox has been renamed or deleted while
+\fBimapsync\fR wasn't running is done by looking for a mailbox with same
+UIDVALIDITY.  [RFC3501] describes the purpose of UIDVALIDITY as to let
+clients know when to invalidate their UID cache.  In particular, there
+is no requirement that two mailboxes can't share same UIDVALIDITY.
+However such a possibility would defeat \fBimapsync\fR's heuristic to
+detect whether a mailbox has been renamed or deleted offline.
+.IP \[bu]
+\fBimapsync\fR is single threaded and doesn't use IMAP command
+pipelining.  Performance improvement could be achieved by sending
+independent commands to each server in parallel, and for a given server,
+by sending independent commands (such as flag updates) in a pipeline.
+.IP \[bu]
+Because the IMAP protocol doesn't have a specific response code for when
+a message is moved to another mailbox (using the MOVE command from
+[RFC6851] or COPY + STORE + EXPUNGE), moving a messages causes
+\fBimapsync\fR to believe that it was deleted while another one (which
+is replicated again) was added to the other mailbox in the meantime.
+
+.IP \[bu]
+\(lqPLAIN\(rq and \(lqLOGIN\(rq are the only authentication mechanisms
+currently supported.
+
+.SH AUTHOR
+Guilhem Moulin <guilhem@fripost.org>
diff --git a/imapsync.sample b/imapsync.sample
index 51958aa..e563e94 100644
--- a/imapsync.sample
+++ b/imapsync.sample
@@ -1,7 +1,7 @@
 ; database = imap.guilhem.org.db
 
 [local]
-type = preauth
+type = tunnel
 command = /usr/lib/dovecot/imap
 
 [remote]
@@ -12,9 +12,9 @@ username = guilhem
 password = xxxxxxxxxxxxxxxx
 
 ; SSL options
-;SSL_verify_peer = TRUE
-SSL_ca_path = /etc/ssl/certs
 ;SSL_cipher_list = EECDH+AES:EDH+AES:!MEDIUM:!LOW:!EXP:!aNULL:!eNULL:!SSLv2:!SSLv3:!TLSv1:!TLSv1.1
 ;SSL_fingerprint = sha256$62E436BB329C46A628314C49BDA7C2A2E86C57B2021B9A964B8FABB6540D3605
+;SSL_verify_trusted_peer = YES
+SSL_ca_path = /etc/ssl/certs
 
 ; vim:ft=dosini
diff --git a/lib/Net/IMAP/Sync.pm b/lib/Net/IMAP/Sync.pm
index 362d436..9db339b 100644
--- a/lib/Net/IMAP/Sync.pm
+++ b/lib/Net/IMAP/Sync.pm
@@ -39,17 +39,17 @@ my $RE_TEXT_CHAR    = qr/[\x01-\x09\x0B\x0C\x0E-\x7F]/;
 my %OPTIONS = (
     host => qr/\A([0-9a-zA-Z:.-]+)\z/,
     port => qr/\A([0-9]+)\z/,
-    type => qr/\A(imaps?|preauth)\z/,
-    STARTTLS => qr/\A(true|false)\z/i,
+    type => qr/\A(imaps?|tunnel)\z/,
+    STARTTLS => qr/\A(YES|NO)\z/i,
     username => qr/\A([\x01-\x7F]+)\z/,
     password => qr/\A([\x01-\x7F]+)\z/,
     auth => qr/\A($RE_ATOM_CHAR+(?: $RE_ATOM_CHAR+)*)\z/,
-    command => qr/\A(\P{Control}+)\z/,
-    'read-only' => qr/\A(TRUE|FALSE)\z/i,
-    SSL_ca_path => qr/\A(\P{Control}+)\z/,
-    SSL_cipher_list => qr/\A(\P{Control}+)\z/,
+    command => qr/\A(\/\P{Control}+)\z/,
+    'read-only' => qr/\A(YES|NO)\z/i,
     SSL_fingerprint => qr/\A([A-Za-z0-9]+\$\p{AHex}+)\z/,
-    SSL_verify_peer => qr/\A(TRUE|FALSE)\z/i,
+    SSL_cipher_list => qr/\A(\P{Control}+)\z/,
+    SSL_verify_trusted_peer => qr/\A(YES|NO)\z/i,
+    SSL_ca_path => qr/\A(\P{Control}+)\z/,
 );
 
 
@@ -87,7 +87,7 @@ sub read_config($$%) {
         $conf->{host} //= 'localhost';
         $conf->{port} //= $conf->{type} eq 'imaps' ? 993 : $conf->{type} eq 'imap' ? 143 : undef;
         $conf->{auth} //= 'PLAIN LOGIN';
-        $conf->{STARTTLS} //= 'TRUE';
+        $conf->{STARTTLS} //= 'YES';
 
         # untaint and validate the config
         foreach my $k (keys %$conf) {
@@ -203,7 +203,7 @@ our $IMAP_text;
 #
 #   - 'enable': An extension or array reference of extensions to ENABLE
 #     (RFC 5161) after entering AUTH state.  Croak if the server did not
-#     advertize "ENABLE" in its CAPABILITY list or does not reply with
+#     advertise "ENABLE" in its CAPABILITY list or does not reply with
 #     an untagged ENABLED response with all the given extensions.
 #
 #   - 'STDERR': Where to log debug and informational messages (default:
@@ -225,7 +225,7 @@ sub new($%) {
     bless $self, $class;
 
     # whether we're allowed to to use read-write command
-    $self->{'read-only'} = uc ($self->{'read-only'} // 'FALSE') ne 'TRUE' ? 0 : 1;
+    $self->{'read-only'} = uc ($self->{'read-only'} // 'NO') ne 'YES' ? 0 : 1;
 
     # where to log
     $self->{STDERR} //= \*STDERR;
@@ -234,10 +234,10 @@ sub new($%) {
     # (cf RFC 3501 section 3)
     $self->{_STATE} = '';
 
-    if ($self->{type} eq 'preauth') {
+    if ($self->{type} eq 'tunnel') {
         require 'IPC/Open2.pm';
-        my $command = $self->{command} // $self->fail("Missing preauth command");
-        my $pid = IPC::Open2::open2(@$self{qw/STDOUT STDIN/}, split(/ /, $command))
+        my $command = $self->{command} // $self->fail("Missing tunnel command");
+        my $pid = IPC::Open2::open2(@$self{qw/STDOUT STDIN/}, $command)
             or $self->panic("Can't fork: $!");
     }
     else {
@@ -252,8 +252,8 @@ sub new($%) {
         }
         else {
             require 'IO/Socket/SSL.pm';
-            if (defined (my $vrfy = delete $self->{SSL_verify_peer})) {
-                $args{SSL_verify_mode} = 0 if uc $vrfy eq 'FALSE';
+            if (defined (my $vrfy = delete $self->{SSL_verify_trusted_peer})) {
+                $args{SSL_verify_mode} = 0 if uc $vrfy eq 'NO';
             }
             my $fpr = delete $self->{SSL_fingerprint};
             $args{$_} = $self->{$_} foreach grep /^SSL_/, keys %$self;
@@ -311,16 +311,16 @@ sub new($%) {
         $self->{_STATE} = 'UNAUTH';
         my @caps = $self->capabilities();
 
-        if ($self->{type} eq 'imap' and uc $self->{STARTTLS} ne 'FALSE') { # RFC 2595 section 5.1
-            $self->fail("Server did not advertize STARTTLS capability.")
+        if ($self->{type} eq 'imap' and uc $self->{STARTTLS} ne 'NO') { # RFC 2595 section 5.1
+            $self->fail("Server did not advertise STARTTLS capability.")
                 unless grep {$_ eq 'STARTTLS'} @caps;
 
             require 'IO/Socket/SSL.pm';
             $self->_send('STARTTLS');
 
             my %sslargs;
-            if (defined (my $vrfy = delete $self->{SSL_verify_peer})) {
-                $sslargs{SSL_verify_mode} = 0 if uc $vrfy eq 'FALSE';
+            if (defined (my $vrfy = delete $self->{SSL_verify_trusted_peer})) {
+                $sslargs{SSL_verify_mode} = 0 if uc $vrfy eq 'NO';
             }
             my $fpr = delete $self->{SSL_fingerprint};
             $sslargs{$_} = $self->{$_} foreach grep /^SSL_/, keys %$self;
@@ -373,7 +373,7 @@ sub new($%) {
                    : ref $self->{enable} eq 'ARRAY' ? @{$self->{enable}}
                    : ($self->{enable});
     if (@extensions) {
-        $self->fail("Server did not advertize ENABLE (RFC 5161) capability.") unless $self->_capable('ENABLE');
+        $self->fail("Server did not advertise ENABLE (RFC 5161) capability.") unless $self->_capable('ENABLE');
         $self->_send('ENABLE '.join(' ',@extensions));
         my @enabled = @{$self->{_ENABLED} // []};
         $self->fail("Couldn't ENABLE $_") foreach
@@ -451,7 +451,7 @@ sub capabilities($) {
 
 # $self->incapable(@capabilities)
 #   In list context, return the list capabilties from @capabilities
-#   which were NOT advertized by the server.  In scalar context, return
+#   which were NOT advertised by the server.  In scalar context, return
 #   the length of said list.
 sub incapable($@) {
     my ($self, @caps) = @_;
@@ -569,7 +569,7 @@ sub list($$@) {
 
 
 # $self->remove_message($uid, [...])
-#   Remove the given $uid list.  Croak if the server did not advertize
+#   Remove the given $uid list.  Croak if the server did not advertise
 #   "UIDPLUS" (RFC 4315) in its CAPABILITY list.
 #   Successfully EXPUNGEd UIDs are removed from the pending VANISHED and
 #   MODIFIED lists.
@@ -577,7 +577,7 @@ sub list($$@) {
 sub remove_message($@) {
     my $self = shift;
     my @set = @_;
-    $self->fail("Server did not advertize UIDPLUS (RFC 4315) capability.")
+    $self->fail("Server did not advertise UIDPLUS (RFC 4315) capability.")
         if $self->incapable('UIDPLUS');
 
     my $set = compact_set(@set);
@@ -609,8 +609,8 @@ sub remove_message($@) {
 
 # $self->append($mailbox, $mail, [...])
 #   Issue an APPEND command with the given mails.  Croak if the server
-#   did not advertize "UIDPLUS" (RFC 4315) in its CAPABILITY list.
-#   Providing multiple mails is only allowed for servers advertizing
+#   did not advertise "UIDPLUS" (RFC 4315) in its CAPABILITY list.
+#   Providing multiple mails is only allowed for servers advertising
 #   "MULTIAPPEND" (RFC 3502) in their CAPABILITY list.
 #   Return the list of UIDs allocated for the new messages.
 sub append($$@) {
@@ -618,7 +618,7 @@ sub append($$@) {
     my $mailbox = shift;
     return unless @_;
     $self->fail("Server is read-only.") if $self->{'read-only'};
-    $self->fail("Server did not advertize UIDPLUS (RFC 4315) capability.")
+    $self->fail("Server did not advertise UIDPLUS (RFC 4315) capability.")
         if $self->incapable('UIDPLUS');
 
     my @appends;
@@ -630,7 +630,7 @@ sub append($$@) {
         $append .= "{".length($mail->{RFC822})."}\r\n".$mail->{RFC822};
         push @appends, $append;
     }
-    $self->fail("Server did not advertize MULTIAPPEND (RFC 3502) capability.")
+    $self->fail("Server did not advertise MULTIAPPEND (RFC 3502) capability.")
         if $#appends > 0 and $self->incapable('MULTIAPPEND');
 
     # dump the cache before issuing the command if we're appending to the current mailbox
@@ -692,10 +692,10 @@ sub fetch($$$$) {
 # $self->notify(@specifications)
 #   Issue a NOTIFY command with the given mailbox @specifications (cf RFC
 #   5465 section 6) to be monitored.  Croak if the server did not
-#   advertize "NOTIFY" (RFC 5465) in its CAPABILITY list.
+#   advertise "NOTIFY" (RFC 5465) in its CAPABILITY list.
 sub notify($@) {
     my $self = shift;
-    $self->fail("Server did not advertize NOTIFY (RFC 5465) capability.")
+    $self->fail("Server did not advertise NOTIFY (RFC 5465) capability.")
         if $self->incapable('NOTIFY');
     my $events = join ' ', qw/MessageNew MessageExpunge FlagChange MailboxName SubscriptionChange/;
     # Be notified of new messages with EXISTS/RECENT responses, but
@@ -1216,7 +1216,7 @@ sub _select_or_examine($$$) {
            ($pcache->{HIGHESTMODSEQ} // 0) > 0 and ($pcache->{UIDNEXT} // 1) > 1;
 
     if ($self->{_STATE} eq 'SELECTED' and ($self->_capable('CONDSTORE') or $self->_capable('QRESYNC'))) {
-        # A mailbox is currently selected and the server advertizes
+        # A mailbox is currently selected and the server advertises
         # 'CONDSTORE' or 'QRESYNC' (RFC 7162).  Delay the mailbox
         # selection until the [CLOSED] response code has been received:
         # all responses before the [CLOSED] response code refer to the