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Diffstat (limited to 'README')
| -rw-r--r-- | README | 89 |
1 files changed, 43 insertions, 46 deletions
@@ -1,54 +1,51 @@ InterIMAP is a fast bidirectional synchronization program for QRESYNC-capable IMAP4rev1 servers. PullIMAP retrieves messages a remote IMAP mailbox and -deliver them to an SMTP session. Visit https://guilhem.org/interimap -for more information. +deliver them to an SMTP session. Visit https://guilhem.org/interimap for more +information. -_______________________________________________________________________ +______________________________________________________________________________ -Compared to IMAP-to-Maildir synchronization solutions like OfflineIMAP, -adding an IMAP server between the Maildir storage and the MUA saves -loads of readdir(2) system calls and other File System quirks; moreover -the abstraction layer offered by the IMAP server makes the MUA and -synchronization program agnostic to the storage backend (Maildir, mbox, -dbox,...) in use. +Compared to IMAP-to-Maildir synchronization solutions like OfflineIMAP, adding +an IMAP server between the Maildir storage and the MUA saves loads of +readdir(2) system calls and other File System quirks; moreover the abstraction +layer offered by the IMAP server makes the MUA and synchronization program +agnostic to the storage backend (Maildir, mbox, dbox,...) in use. IMAP synchronization of a mailbox is usually two-folds: 1/ detect and -propagate changes (flag updates and message deletions) to existing -messages, then 2/ copy the new messages. The naive way to perform the -first step is to issue a FETCH command to list all messages in the -mailbox along with their flags and UIDs, causing heavy network usage. -Instead, InterIMAP takes advantage of the QRESYNC extension from -[RFC7162] to perform stateful synchronization: querying changes since -the last synchronization only gives a phenomenal performance boost and -drastically reduces the network traffic. +propagate changes (flag updates and message deletions) to existing messages, +then 2/ copy the new messages. The naive way to perform the first step is to +issue a FETCH command to list all messages in the mailbox along with their +flags and UIDs, causing heavy network usage. Instead, InterIMAP takes +advantage of the QRESYNC extension from [RFC7162] to perform stateful +synchronization: querying changes since the last synchronization only gives a +phenomenal performance boost and drastically reduces the network traffic. -For convenience reasons servers must also support LIST-EXTENDED -[RFC5258], LIST-STATUS [RFC5819] and UIDPLUS [RFC4315]. Other supported -extensions are: - * LITERAL+ [RFC2088] non-synchronizing literals (recommended), - * MULTIAPPEND [RFC3502] (recommended), - * COMPRESS=DEFLATE [RFC4978] (recommended), - * SASL-IR [RFC4959] SASL Initial Client Response, and +For convenience reasons servers must also support LIST-EXTENDED [RFC5258], +LIST-STATUS [RFC5819] and UIDPLUS [RFC4315]. Other supported extensions are: + + * LITERAL+ [RFC2088] non-synchronizing literals (recommended); + * MULTIAPPEND [RFC3502] (recommended); + * COMPRESS=DEFLATE [RFC4978] (recommended); + * SASL-IR [RFC4959] SASL Initial Client Response; and * UNSELECT [RFC3691]. -_______________________________________________________________________ +______________________________________________________________________________ -IMAP traffic is mostly text (beside message bodies perhaps) hence -compresses pretty well: enabling compression can save a great amount of -network resources. +IMAP traffic is mostly text (beside message bodies perhaps) hence compresses +pretty well: enabling compression can save a great amount of network +resources. However establishing an SSL/TLS connection (type=imaps, or type=imap and STARTTLS=YES) yields a small overhead due to the SSL/TLS handshake. On the other hand if SSH access is allowed on the remote server, one can -tunnel the IMAP traffic through SSH and use OpenSSH's ControlPersist -feature to save most of the cryptographic overhead (at the expense of a -local 'ssh' process and a remote 'imap' process). Moreover if the IMAP -user is a valid UNIX user it is possible to use pre-authentication on -the remote server as well, which saves the extra round trip caused by -the AUTHENTICATE command. For instance the following configuration -snippet saves bandwidth and brings a significant speed gain compared to -type=imaps. +tunnel the IMAP traffic through SSH and use OpenSSH's ControlPersist feature +to save most of the cryptographic overhead (at the expense of a local 'ssh' +process and a remote 'imap' process). Moreover if the IMAP user is a valid +UNIX user it is possible to use pre-authentication on the remote server as +well, which saves the extra round trip caused by the AUTHENTICATE command. +For instance the following configuration snippet saves bandwidth and brings a +significant speed gain compared to type=imaps. local: $XDG_CONFIG_HOME/interimap/config: [remote] @@ -71,15 +68,15 @@ type=imaps. remote: ~user/.ssh/authorized_keys: restrict,command="/usr/bin/doveadm exec imap" ssh-[…] id-interimap -However for long-lived connections (using the --watch command-line -option), the TLS overhead becomes negligible hence the advantage offered -by the OpenSSH ControlPersist feature is not obvious. Furthermore if -the remote server supports the IMAP COMPRESS extension [RFC4978], adding -compress=DEFLATE to the configuration can also greatly reduce bandwidth -usage with regular INET sockets (type=imaps or type=imap). +However for long-lived connections (using the --watch command-line option), +the TLS overhead becomes negligible hence the advantage offered by the OpenSSH +ControlPersist feature is not obvious. Furthermore if the remote server +supports the IMAP COMPRESS extension [RFC4978], adding compress=DEFLATE to the +configuration can also greatly reduce bandwidth usage with regular INET +sockets (type=imaps or type=imap). -_______________________________________________________________________ +______________________________________________________________________________ -InterIMAP is Copyright© 2015-2020 Guilhem Moulin ⟨guilhem@fripost.org⟩, -and licensed for use under the GNU General Public License version 3 or -later. See ‘COPYING’ for specific terms and distribution information. +InterIMAP is Copyright© 2015-2020 Guilhem Moulin ⟨guilhem@fripost.org⟩, and +licensed for use under the GNU General Public License version 3 or later. See +‘COPYING’ for specific terms and distribution information. |