Name

PullIMAP - Pull mails from an IMAP mailbox and deliver them to an SMTP session

Synopsis

pullimap [--config=FILE] [--idle[=SECONDS]] [--no-delivery] [--quiet] SECTION

Description

pullimap retrieves messages from an IMAP mailbox and deliver them to an 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 section below for details.

Options

--config=FILE

Specify an alternate configuration file. Relative paths start from $XDG_CONFIG_HOME/pullimap, or ~/.config/pullimap 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 command-line option, pullimap reads its configuration from $XDG_CONFIG_HOME/pullimap/config (or ~/.config/pullimap/config 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 (UTF-7 encoded and unquoted) 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 and LMTP servers are supported, and SMTP pipelining 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. Note that the local part needs to quoted if it contains special characters; see RFC 5321 for details. (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 (or extended SEARCH on servers advertizing the ESEARCH capability) 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 an INET socket. type=tunnel causes pullimap to create an unnamed pair of connected sockets for interprocess communication with a command instead of opening a network 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 is supported (with optional username/password authentication), 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 on its standard output, and understand it on its standard input. The value is passed to `/bin/sh -c` if it contains shell metacharacters; otherwise it is split into words and the resulting list is passed to execvp(3).

STARTTLS

Whether to use the STARTTLS 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 types 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 for servers advertising it. (Default: YES.)

null-stderr

Whether to redirect command’s standard error to /dev/null for 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, TLSv1.2, and TLSv1.3. Enabling a protocol is a short-hand for disabling all other protocols. (Default: !SSLv2 !SSLv3 !TLSv1 !TLSv1.1, i.e., only enable TLSv1.2 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’s Subject Public Key Info, in the form [ALGO$]DIGEST_HEX where ALGO is the used algorithm (by default sha256). Attempting to connect to a server with a non-matching certificate SPKI fingerprint causes pullimap to abort the connection during the SSL/TLS handshake. The following command can be used to compute the SHA-256 digest of a certificate’s Subject Public Key Info:

openssl x509 -in /path/to/server/certificate.pem -pubkey \
| openssl pkey -pubin -outform DER \
| openssl dgst -sha256
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 does not guaranty that untagged FETCH responses are sent ordered by UID in response to a 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 RFC822 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 a UID FETCH command to retrieve message ENVELOPE and RFC822 (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:

    1. 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 (the channel is kept open and shared for all messages retrieved while the UID FETCH IMAP command is in progress);

    2. perform a mail transaction (using SMTP pipelining if possible) to deliver the retrieved message RFC822 body to the SMTP or LMTP session; and

    3. append the message UID to the statefile.

  2. If an SMTP/LMTP transmission channel was opened, send a QUIT command to terminate it gracefully.

  3. Issue a 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 when a new message is received (or when the IDLE timeout expires).

Standards