Node.js program that masks an IMAP server behind a simple POP3 server.

Requires the imap module (amongst others).

Setting up a server

Imask reads options from a configuration file, by default ~/.imask. To read from a different configuration file, pass the file name as the sole command line argument.

The configuration file is a JSON dictionary, e.g.:

{
    "logFile": "~/mylogfile",

    "popPort": "110",
    "popUseSSL": true,
    "popSSLKeyFile": "~/server-key.pem",
    "popSSLCertFile": "~/server-cert.pem",

    "accounts": {
        "pop_user_1_username": {
            "popPassword": "pop_user_1_password",
            "imapHost": "imap.xxx.xxx",
            "imapPort": 143,
            "imapUseSSL": false,
            "imapUsername": "my_email_username",
            "imapPassword": "my_email_password",
            "imapMailboxes": ["INBOX", "Some mailing list"],
            "imapPollIntervalSeconds": 180,
            "imapReadOnly": false,
            "imapMessageAgeLimitDays": 30
        },
        "pop_user_2_username": {
            "popPassword": "pop_user_2_password",
            "imapHost": "imap.xxx.xxx",
            "imapPort": 993,
            "imapUseSSL": true,
            "imapUsername": "my_email_username",
            "imapPassword": "my_email_password",
            "imapMailboxes": ["INBOX"],
            "imapPollIntervalSeconds": 180,
            "imapReadOnly": false,
            "imapMessageAgeLimitDays": 30
        },
    },

    "webLogsUsername": "choose_a_username",
    "webLogsPassword": "choose_a_password",
    "webLogsPort": 5000,
    "webLogsMaxLines": 50,
    "webLogsSSLKeyFile": "~/server-key.pem",
    "webLogsSSLCertFile": "~/server-cert.pem"
}

Lines beggining with # are stripped prior to the JSON parse. The popUseSSL key can be set to true to have the POP server use SSL. If the imapUseSSL key is set to true, imask attempts to connect to the IMAP server over SSL. If no log file is specified, imask logs to stdout and stderr. Once the configuration file is set up imask can be started as follows:

node imask.js

Or with the configuration file explicitly specified:

node imask.js /my/configuration/file

POP/IMAP interaction

Messages which are retrieved from the POP server are marked as unseen (i.e. unread) on the IMAP server, unless imapReadOnly is true. Applications connecting to the POP server must use PASS authentication with one of the username/password pairs specified in the configuration file.

The imapMessageAgeLimitDays option can be used to stop imask retrieving old messages from the IMAP server, even if they are unread. This can be set to a null value if you want all messages to be retrieved regardless of age. Note that if imapReadOnly is true (so that messages retrieved via the pop server are not marked as read on the IMAP server), then an age limit really should be set, or imask will repeatedly download an ever-increasing set of messages.

Imask uses the IMAP id of each message to provide a unique identifier via the UIDL extension to POP. Imask operates on the assumption that the POP client will use UIDL to ensure that duplicate messages do not appear in the inbox if imask is restarted. (I.e., imask does not attempt to save any state allowing it to determine which messages were retrieved via the pop server the last time it was run.) In the case of GMail's POP client, this appears to work.

Imask stores everything in memory and does not write anything to disk (except the log file).

Web accessible logs

If the webLogs* options are set, imask provides https access to recent log entries. The number of lines stored is determined by webLogsMaxLines. Lines are stored in memory, so this value should not be enormous. To view the logs, access the http server at the specified port, which will present a login form. If the webLogs* options are not set, imask can be run without installing express and the various modules which it depends on.

Why you might want this

GMail can automatically poll a POP server for mail, but not an IMAP server. If your mail provider only provides IMAP, imask can be used to provide a POP server for GMail to poll. (Although, if you have your own server, you should also be able to use fetchmail to download mail from the IMAP server and then pass it on to GMail's SMTP server -- I got bored trying to make this work.)