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diff --git a/pullimap.md b/pullimap.md new file mode 100644 index 0000000..54c6ce5 --- /dev/null +++ b/pullimap.md @@ -0,0 +1,355 @@ +% pullimap(1) +% [Guilhem Moulin](mailto:guilhem@fripost.org) +% March 2016 + +Name +==== + +PullIMAP - Pull mails from an IMAP mailbox and deliver them to a SMTP +session + +Synopsis +======== + +`pullimap` [**\-\-config=***FILE*] [**\-\-idle**[**=***SECONDS*]] +[**\-\-no-delivery**] [**\-\-quiet**] *SECTION* + +Description +=========== + +`pullimap` retrieves messages from an IMAP mailbox and deliver them to a +SMTP or LMTP transmission channel. It can also remove old messages +after a configurable retention period. + +A *statefile* is used to keep track of the mailbox's `UIDVALIDITY` and +`UIDNEXT` values. While `pullimap` is running, the *statefile* is also +used to keep track of UIDs being delivered, which avoids duplicate +deliveries in case the process is interrupted. +See the [**Control flow**](#control-flow) section below for details. + +Options +======= + +`--config=`*FILE* + +: Specify an alternate configuration file. Relative paths start from + *$XDG_CONFIG_HOME*, or *~/.config* if the `XDG_CONFIG_HOME` + environment variable is unset. + +`--idle`[`=`*seconds*] + +: Don't exit after a successful poll. Instead, keep the connection open + and issue `IDLE` commands (require an IMAP server supporting [RFC + 2177]) to watch for updates in the mailbox. This also enables + `SO_KEEPALIVE` on the socket. Each `IDLE` command is terminated after + at most *seconds* (29 minutes by default) to avoid being logged out + for inactivity. + +`--no-delivery` + +: Update the *statefile*, but skip SMTP/LMTP delivery. This is mostly + useful for initializing the *statefile* when migrating to + `pullimap` from another similar program such as [`fetchmail`(1)] or + [`getmail`(1)]. + +`-q`, `--quiet` + +: Try to be quiet. + +`--debug` + +: Turn on debug mode. Debug messages are written to the error output. + Note that this include all IMAP traffic (except literals). Depending + on the chosen authentication mechanism, this might include + authentication credentials. + +`-h`, `--help` + +: Output a brief help and exit. + +`--version` + +: Show the version number and exit. + + +Configuration file +================== + +Unless told otherwise by the `--config=FILE` option, `pullimap` reads +its configuration from *$XDG_CONFIG_HOME/pullimap* (or +*~/.config/pullimap* if the `XDG_CONFIG_HOME` environment variable is +unset) as an [INI file]. +The syntax of the configuration file is a series of `OPTION=VALUE` +lines organized under some `[SECTION]`; lines starting with a ‘#’ or +‘;’ character are ignored as comments. +Valid options are: + +*statefile* + +: State file to use to keep track of the *mailbox*'s `UIDVALIDITY` and + `UIDNEXT` values. Relative paths start from + *$XDG_DATA_HOME/pullimap*, or *~/.local/share/pullimap* if the + `XDG_DATA_HOME` environment variable is unset. + (Default: the parent section name of the option.) + +*mailbox* + +: The IMAP mailbox to pull messages from. + Support for persistent message Unique Identifiers (UID) is required. + (Default: `INBOX`.) + +*deliver-method* + +: `PROTOCOL:[ADDRESS]:PORT` where to deliver messages. Both [SMTP][RFC + 5321] and [LMTP][RFC 2033] servers are supported, and [SMTP + pipelining][RFC 2920] is used when possible. + (Default: `smtp:[127.0.0.1]:25`.) + +*deliver-ehlo* + +: Hostname to use in `EHLO` or `LHLO` commands. + (Default: `localhost.localdomain`.) + +*deliver-rcpt* + +: Message recipient. + (Default: the username associated with the effective uid of the + `pullimap` process.) + +*purge-after* + +: Retention period (in days), after which messages are removed from the + IMAP server. (The value is at best 24h accurate due to the IMAP + `SEARCH` criterion ignoring time and timezone.) + If *purge-after* is set to `0` then messages are deleted immediately + after delivery. Otherwise `pullimap` issues an IMAP `SEARCH` command + to list old messages; if `--idle` is set then the `SEARCH` command is + issued again every 12 hours. + +*type* + +: One of `imap`, `imaps` or `tunnel`. + `type=imap` and `type=imaps` are respectively used for IMAP and IMAP + over SSL/TLS connections over a INET socket. + `type=tunnel` causes `pullimap` to open a pipe to a *command* instead + of a raw socket. + (Default: `imaps`.) + +*host* + +: Server hostname, for `type=imap` and `type=imaps`. + (Default: `localhost`.) + +*port* + +: Server port. + (Default: `143` for `type=imap`, `993` for + `type=imaps`.) + +*proxy* + +: An optional SOCKS proxy to use for TCP connections to the IMAP server + (`type=imap` and `type=imaps` only), formatted as + `PROTOCOL://[USER:PASSWORD@]PROXYHOST[:PROXYPORT]`. + If `PROXYPORT` is omitted, it is assumed at port 1080. + Only [SOCKSv5][RFC 1928] is supported (with optional + [username/password authentication][RFC 1929]), in two flavors: + `socks5://` to resolve *hostname* locally, and `socks5h://` to let the + proxy resolve *hostname*. + +*command* + +: Command to use for `type=tunnel`. Must speak the [IMAP4rev1 + protocol][RFC 3501] on its standard output, and understand it on its + standard input. + +*STARTTLS* + +: Whether to use the [`STARTTLS`][RFC 2595] directive to upgrade to a + secure connection. Setting this to `YES` for a server not advertising + the `STARTTLS` capability causes `pullimap` to immediately abort the + connection. + (Ignored for *type*s other than `imap`. Default: `YES`.) + +*auth* + +: Space-separated list of preferred authentication mechanisms. + `pullimap` uses the first mechanism in that list that is also + advertised (prefixed with `AUTH=`) in the server's capability list. + Supported authentication mechanisms are `PLAIN` and `LOGIN`. + (Default: `PLAIN LOGIN`.) + +*username*, *password* + +: Username and password to authenticate with. Can be required for non + pre-authenticated connections, depending on the chosen authentication + mechanism. + +*compress* + +: Whether to use the [`IMAP COMPRESS` extension][RFC 4978] for servers + advertising it. (Default: `YES`.) + +*null-stderr* + +: Whether to redirect *command*'s standard error to `/dev/null` for type + `type=tunnel`. (Default: `NO`.) + +*SSL_protocols* + +: A space-separated list of SSL protocols to enable or disable (if + prefixed with an exclamation mark `!`. Known protocols are + `SSLv2`, `SSLv3`, `TLSv1`, `TLSv1.1`, and `TLSv1.2`. Enabling a + protocol is a short-hand for disabling all other protocols. + (Default: `!SSLv2 !SSLv3`, i.e., only enable TLSv1 and above.) + +*SSL_cipher_list* + +: The cipher list to send to the server. Although the server determines + which cipher suite is used, it should take the first supported cipher + in the list sent by the client. See [`ciphers`(1ssl)] for more + information. + +*SSL_fingerprint* + +: Fingerprint of the server certificate (or its public key) in the form + `ALGO$DIGEST_HEX`, where `ALGO` is the used algorithm (default + `sha256`). + Attempting to connect to a server with a non-matching certificate + fingerprint causes `pullimap` to abort the connection during the + SSL/TLS handshake. + +*SSL_verify* + +: Whether to verify the server certificate chain. + Note that using *SSL_fingerprint* to specify the fingerprint of the + server certificate is an orthogonal authentication measure as it + ignores the CA chain. + (Default: `YES`.) + +*SSL_CApath* + +: Directory to use for server certificate verification if + `SSL_verify=YES`. + This directory must be in “hash format”, see [`verify`(1ssl)] for + more information. + +*SSL_CAfile* + +: File containing trusted certificates to use during server certificate + authentication if `SSL_verify=YES`. + +Control flow +============ + +`pullimap` opens the *statefile* corresponding to a given configuration +*SECTION* with `O_DSYNC` to ensure that written data is flushed to the +underlying hardware by the time [`write`(2)] returns. Moreover an +exclusive lock is placed on the file descriptor immediately after +opening to prevent multiple `pullimap` processes from accessing the +*statefile* concurrently. + +Each *statefile* consists of a series of 32-bits big-endian integers. +Usually there are only two integers: the first is the *mailbox*'s +`UIDVALIDITY` value, and the second is the *mailbox*'s last seen +`UIDNEXT` value (`pullimap` then assumes that all messages with UID +smaller than this `UIDNEXT` value have already been retrieved and +delivered). +The [IMAP4rev1 specification][RFC 3501] does not guaranty that untagged +`FETCH` responses are sent ordered by UID in response to an `UID FETCH` +command. Thus it would be unsafe for `pullimap` to update the `UIDNEXT` +value in its *statefile* while the `UID FETCH` command is progress. +Instead, for each untagged `FETCH` response received while the `UID +FETCH` command is in progress, `pullimap` delivers the message `BODY` to +the SMTP or LMTP server (specified with *deliver-method*) then appends +the message UID to the *statefile*. +When the `UID FETCH` command eventually terminates, `pullimap` updates +the `UIDNEXT` value in the *statefile* and truncate the file down to 8 +bytes. Keeping track of message UIDs as they are received avoids +duplicate in the event of a crash or connection loss while the `UID +FETCH` command is in progress. + +In more details, `pullimap` works as follows: + + 1. Issue an `UID FETCH` command to retrieve message `ENVELOPE` and + `BODY` (and `UID`) with UID bigger or equal than the `UIDNEXT` value + found in the *statefile*. + While the `UID FETCH` command is in progress, perform the following + for each untagged `FETCH` response sent by the server: + + i) if no SMTP/LMTP transmission channel was opened, open one to the + server specified with *deliver-method* and send an `EHLO` (or + `LHO`) command with the domain specified by *deliver-ehlo*; + + ii) perform a mail transaction (using [SMTP pipelining][RFC 2920] if + possible) to send the retrieved message BODY to the SMTP or LMTP + session; and + + ii) append the message UID to the *statefile*. + + 2. If a SMTP/LMTP transmission channel was opened, send a `QUIT` command + to terminate it gracefully. + + 3. Issue an `UID STORE` command to mark all retrieved messages (and + stalled UIDs found in the *statefile* after the eigth byte) as + `\Seen`. + + 4. Update the *statefile* with the new UIDNEXT value (bytes 5-8). + + 5. Truncate the *statefile* down to 8 bytes (so that it contains only + two 32-bits integers, respectively the *mailbox*'s current + `UIDVALIDITY` and `UIDNEXT` values). + + 6. If `--idle` was set, issue an `IDLE` command; stop idling and go + back to step 1. whenever a new message is received. + +Standards +========= + + * M. Leech, M. Ganis, Y. Lee, R. Kuris, D. Koblas and L. Jones, + _SOCKS Protocol Version 5_, + [RFC 1928], March 1996 + * M. Leech, _Username/Password Authentication for SOCKS V5_, + [RFC 1929], March 1996 + * J. Myers, _Local Mail Transfer Protocol_, + [RFC 2033], October 1996 + * J. Myers, _IMAP4 non-synchronizing literals_, + [RFC 2088], January 1997 + * B. Leiba, _IMAP4 IDLE command_, + [RFC 2177], June 1997 + * C. Newman, _Using TLS with IMAP, POP3 and ACAP_, + [RFC 2595], June 1999 + * N. Freed, _SMTP Service Extension for Command Pipelining_, + [RFC 2920], September 2000 + * M. Crispin, _Internet Message Access Protocol - Version 4rev1_, + [RFC 3501], March 2003 + * M. Crispin, + _Internet Message Access Protocol (IMAP) - UIDPLUS extension_, + [RFC 4315], December 2005 + * A. Gulbrandsen, _The IMAP COMPRESS Extension_, + [RFC 4978], August 2007 + * R. Siemborski and A. Gulbrandsen, _IMAP Extension for Simple + Authentication and Security Layer (SASL) Initial Client Response_, + [RFC 4959], September 2007 + * J. Klensin, _Simple Mail Transfer Protocol_, + [RFC 5321], October 2008 + +[RFC 4315]: https://tools.ietf.org/html/rfc4315 +[RFC 2177]: https://tools.ietf.org/html/rfc2177 +[RFC 2595]: https://tools.ietf.org/html/rfc2595 +[RFC 4959]: https://tools.ietf.org/html/rfc4959 +[RFC 2088]: https://tools.ietf.org/html/rfc2088 +[RFC 5321]: https://tools.ietf.org/html/rfc5321 +[RFC 2033]: https://tools.ietf.org/html/rfc2033 +[RFC 2920]: https://tools.ietf.org/html/rfc2920 +[RFC 3501]: https://tools.ietf.org/html/rfc3501 +[RFC 4978]: https://tools.ietf.org/html/rfc4978 +[RFC 1928]: https://tools.ietf.org/html/rfc1928 +[RFC 1929]: https://tools.ietf.org/html/rfc1929 + +[INI file]: https://en.wikipedia.org/wiki/INI_file +[`fetchmail`(1)]: http://www.fetchmail.info/ +[`getmail`(1)]: http://pyropus.ca/software/getmail/ +[`write`(2)]: http://man7.org/linux/man-pages/man2/write.2.html +[`ciphers`(1ssl)]: https://www.openssl.org/docs/manmaster/apps/ciphers.html +[`verify`(1ssl)]: https://www.openssl.org/docs/manmaster/apps/verify.html |