• HowTo
• TriggerGetmailOnIMAPAccess

Triggering getmail on IMAP access

Getmail is a secure, easy-to-use python-based application to retrieve e-mail from a remote mail server and write it immediately to your local maildir store. Many home-based users prefer the 24/7 reliability of their ISP mail server over redirecting e-mail for their domain directly to their home server. Doing so, no e-mail needs to be missed when the home server happens to be down. Standard recommendation is to run getmail in a cron job every 5 minutes or so. This poses two potential problems:

• ISPs are not too happy with this practice, and more importantly,
• The hard disks of your home server will no longer spin down.

Hence, a recurring question on fora is: How can I trigger getmail on IMAP access?

This HOWTO helps you to run getmail only when needed, and have dovecot deliver and filter that mail.

Prerequisites

This HOWTO assumes that you use the IMAP protocol, a Maildir mail store in ~/.maildir, and the "deliver" LDA.

You will also need:

• getmail,

• incron, and a Linux kernel with inotify and flock support.

Using getmail to fetch your remote mail

First, create the directory ~/.getmail, change its permissions with chmod 700 ~/.getmail, and create ~/.getmail/mvmailrc with the following contents:

[retriever]
type = SimpleIMAPSSLRetriever
server = remotehost
port = 993
username = yourusername
password = yourpassword
mailboxes = ('INBOX',)

[destination]
type = MDA_external
path = /usr/lib/dovecot/deliver
arguments = ("-e",)

[options]
read_all = false
delete = true
received = false
delivered_to = false
message_log = ~/.getmail/mvmail.log

Running getmail with this mvmailrc will:

• Log into the imaps server on remotehost on port 993 (use SimpleIMAPRetriever if you do not use SSL) with the specified username and password.

• Retrieve only new mails read_all = false from the remote INBOX folder.

• Pass each mail to Dovecot's LDA "deliver" for filtering and delivery. The -e ensures that dovecot will return an error if filtering or delivery fails; getmail will leave the mail alone if such an error occurs, to prevent you from losing mail.

• Delete mail from your remote INBOX, only after successfully delivering it.

• received = false and delivered_to = false prevent getmail from adding additional headers to your mail.

So, to run getmail and move your mail:

getmail -g ~/.getmail -r mvmailrc

Get mail of virtual accounts

When using getmail to retrieve virtual mail accounts, more configuration is needed. Here is an example of a config file used to retrieve mail for a virtual account:

[retriever]
type = MultidropIMAPSSLRetriever
envelope_recipient = delivered-to:1
server = localhost
port = 993
username = yourusername
password = yourpassword
mailboxes = ("INBOX",)
move_on_delete = .Trash

[destination]
type = MDA_external
path = /usr/local/libexec/dovecot/deliver
arguments = ("-e", "-f", "%(sender)", "-d", "%(recipient)")
user = mailaccess
group = mailaccess

[options]
read_all = false
delete = true
received = false
delivered_to = false
message_log = ~/.getmail/mvmail.log

This file use MultidropIMAPSSLRetriever in order to extract the recipient info in the mail. This is configured in the property envelope_recipient. The recipient must be passed to deliver with the -d parameter as shown with the arguments line. It's important to specify the arguments as separate strings as shown here, not "-d %(recipient)" in one string.

Another important note is that if dovecot.conf is configured to restrict allowed users (first_valid_uid), one might need to specify which user getmail should run as, as shown here with user = mailaccess.

Using incron to get mail only when needed

Running getmail every 5 minutes seems wasteful, since it usually won't have anything to do; it also means you will have to wait 5 minutes for mail to be retrieved when opening your mail reader. With incron, you can instead trigger getmail whenever you access your INBOX. This means that getmail will run immediately when you open your mail reader client, and not run at all when it has nothing to do. After that, it will sleep for 10 minutes to keep your ISP happy.

Create an executable script ~/local/bin/mvmail with the following contents:

#!/bin/bash
DATE=$(date); echo "--- $DATE: mvmail was called. ---" >> ~/.getmail/mvmail.log
flock -n ~/.getmail/mvmail.lock getmail -q -g ~/.getmail/ -r mvmailrc
flock -n ~/.getmail/mvmail.lock DATE=$(date)
flock -n ~/.getmail/mvmail.lock echo "--- $DATE: mvmail went to sleep for 10 minutes. ---" >> ~/.getmail/mvmail.log
flock -n ~/.getmail/mvmail.lock sleep 10m

DATE=$(date); echo "--- $DATE: mvmail rearmed the incron one-shot.  ---" >> ~/.getmail/mvmail.log
incrontab --reload # Rearm the one-shot rule

Run incrontab -e as a normal user -not root- to edit your incrontab, and put this in it:

BEWARE: Do not add any comments nor any additional space characters or tabs! incrontab is very sensitive to this and will not run.

/home/username/.maildir/cur/ IN_ALL_EVENTS,IN_ONESHOT /home/username/local/bin/mvmail

This incrontab will run mvmail whenever you access the INBOX folder. IN_ONESHOT will disable the incron rule after one event, to prevent incron from running one instance of mvmail for every INBOX access. mvmail will then sleep for 10 minutes before finally re-enabling the one-shot incron rule. Every step is logged in ~/.getmail/mvmail.log.