Web-based Email

part of the ArsDigita Community System by Jin Choi

User-accessible directory: /webmail/
Site adminstrator directory: /admin/webmail/
data model: /doc/sql/webmail.sql
procedures: /tcl/webmail-defs

The big picture

In the beginning, email would get sent to your big Unix box and delivered to a central mail queue, where you would pick it up from time to time with your mail reader and store it permanently in your home directory somewhere. You telnetted to the machine, used your favorite mail reader, all your mail was available from one place, it got backed up every night along with everything else on the machine, and life was good.

Then along came POP. Mail was sent to your big Unix box where it got delivered to a central mail queue, from where you would pick it up from time to time with your mail reader. Only now, it would get stored on whatever machine you happened to be at the time that you decided to read it. You could tell it to keep all the mail on the server, but then every time you read your email, you would see things you'd already seen before, even mail you had deleted elsewhere. If you didn't tell it to keep your mail on the server it would get deleted as soon as you picked it up, and the only copy would be on your desktop machine or your laptop, with no backups whatsoever.

IMAP was invented to address this problem, giving both the benefits of POP along with the centralized mail reading convenience of the old-school style of doing things. True, probably your favorite mail reader didn't support IMAP just yet, but you could get by with what was available, and more readers were adding support all the time. Still, you might be stuck somewhere without a readily available IMAP client, and in today's hostile net environment, telnetting to the server in the clear is a no-no. This is where web-based email shines. Constant access to your email store wherever you may be, as long as a web browser is available. Combined with an IMAP interface to the same store, you can have the benefits of both worlds, and be almost as happy as when you were telnetting to your mail server.

This architecture is available today. You can sign up for an account at criticalpath.net, and they will set you up with an IMAP and web-based email account. You can install Oracle email server from a CD and get the same thing. Why yet another system? Ease of modification and flexibility. If you find yourself missing a feature from Critical Path's system that you would dearly love, you can request it of them and they might deign to provide it in the indeterminate future. You may or may not be able to modify the Oracle email system to your particular needs, but I wouldn't know as I haven't been able to figure out how it works. This module is flexible, easy to extend, and easy to understand. Or if not, at least all the source is there for you to look at.

Architecture

As far as possible, I've tried to avoid getting into implementing systems that have been done well before. That means no reinventing of mail software; no implementing of IMAP or SMTP protocols; no worrying about file locking and mail delivery. qmail and the UW IMAP server were written years ago by people who dedicated lots of effort to make sure they were done correctly. This module doesn't even look at email until it has been delivered by qmail as it would be to any user.

Once the mail has been delivered, it is parsed and inserted into Oracle by some Java code running inside Oracle. Using a relational database as the message store has many benefits. It provides a standard data model for multiple interfaces to hook up to. It makes it easy to do the web interface. It is fast and scalable. It makes implementing powerful email search facilities easy. Using Java lets us leverage the JavaMail API to do the hard work of parsing the messages. It also has the benefit of tight integration to Oracle through the JServer JSQL interface. For example, messages are read into a CLOB column by being streamed from the file system in bite sized chunks. If we were using, say, a perl DBI program to do the insertion, we would have to read the entire message into memory before writing it to the CLOB. With multi-megabyte emails becoming more common in today's media-rich environment, this has obvious benefits.

On the front end, we provide a more or less traditional ACS web module for the web-based front end, and an Oracle "driver" (mail store hookup) for the UW IMAP server to provide the IMAP interface (not yet written).

Receiving Mail

The webmail module interfaces with qmail to receive mail. All of the heavy lifting involved in getting email delivered reliably and in a standards-conformant manner is done by qmail.

The webmail system defines domains and email accounts. A domain is defined by a host name and a short string to be able to refer to it easily. The full domain name must correspond to a virtual domain that qmail is set up to receive email for. In the following, let us assume that "webmail.arsdigita.com" is the full domain name and "wm" is the short name.

Set up DNS so that the full domain name resolves to the host on which you are setting up this system (or set up an appropriate MX record).
Add a line consisting of the full domain name to /var/qmail/control/rcpthosts so that qmail knows to receive email for this domain.
Select a name for an email account that will be used to handle all the email for this system. This can be arbitrary, so we will just use "webmail" (if you want to use something else, you must edit the Java code).
Create a virtual user by adding the following line to /var/qmail/users/assign:
```
+webmail-:oracle:101:102:/home/nsadmin/qmail/alias:-::
```
This says any email intended for "webmail-*@webmail.arsdigita.com" will be handled by the Unix user "oracle" (uid 101, gid 102) according to the alias files in the directory /home/nsadmin/qmail/alias. Make sure that directory exists, and can be written to by the nsadmin user:
```
(as root):
mkdirhier /home/nsadmin/qmail/alias
chown nsadmin /home/nsadmin/qmail/alias
```
The location of this alias directory can be changed by setting the AliasDirectory parameter in the webmail section of the ACS .ini file for this server.
Run /var/qmail/bin/qmail-newu to have the previous change take effect.
Add the following to /var/qmail/control/virtualdomains:
```
webmail.arsdigita.com:webmail-wm
```
This tells qmail that any mail sent to "*@webmail.arsdigita.com" will be handled by the webmail virtual user, and have "-wm" appended to the username portion of the email address. So, mail sent to "foo@webmail.arsdigita.com" will be delivered to the webmail user as "webmail-wm@webmail.arsdigita.com".
Register this domain with the webmail system by using the administration pages, with (again, just for this example) "wm" as the short name and "webmail.arsdigita.com" as the domain name. (You will need to load the data model file to do this, which requires that the Java libraries be loaded, see below).
Create a queue directory for deliveries to the webmail user. Make sure it is writable and readable by the oracle Unix account (or whatever user Oracle runs at):
```
(as root:)
/var/qmail/bin/maildirmake /home/nsadmin/qmail/queue
chown -R oracle /home/nsadmin/qmail/queue
```
The location of the queue directory can be changed by setting the QueueDirectory parameter in webmail section of the ACS .ini file for this server.

Once the domain has been set up, you can start adding email accounts. An email account is tied to an ACS user; an ACS user can receive email at any number of different accounts, on any domains that this host receives email for. Once received, they are treated identically, and are indistinguishable other than from the email headers. Email accounts can be assigned to users by using the administration pages.

When an email account is added, a file is created automatically in the alias directory of the form ".qmail-[short domain name]-username" (e.g., ".qmail-wm-jsc") that contains one line with the full path to the queue directory (/home/nsadmin/qmail/queue/). This file specifies that mail sent to "webmail-wm-jsc@webmail.arsdigita.com" be delivered to the maildir directory that we have set up. All email to be handled by the webmail system ends up in the same place (/home/nsadmin/qmail/queue/new). The system uses the RFC822 Delivered-To header to distinguish who it should be displayed to. The indirection through the .qmail alias files is done so that only email sent to valid accounts will be received. Email sent to an address that does not have a .qmail file set up for it will bounce normally.

Once every minute, Oracle polls the new directory of the maildir queue and picks up any mail that has been delivered. Using the JavaMail library running inside Oracle, it stores and parses the message, and saves off various pieces of information (parsed headers, attachments, etc.; see the data model).

To install the Java portion of this module, download the JavaMail library from http://java.sun.com/products/javamail/ and the JavaBeans Activation Framework from http://java.sun.com/beans/glasgow/jaf. Unpack the distributions and load activation.jar and mail.jar into Oracle:

loadjava -user dbuser/dbpasswd -resolve -verbose activation.jar
loadjava -user dbuser/dbpasswd -resolve -verbose mail.jar

(You may get a verification warning attempting to resolve javax/activation/ActivationDataFlavor which you can ignore.) The database user must have been granted the JAVASYSPRIV role.

If you are using Oracle 8.1.5, you will not be able to load the JAF and the JavaMail packages into a user's schema, even with JAVASYSPRIV. You must load them into the SYS schema:
loadjava -user internal/internalpasswd -synonym -resolve -verbose activation.jar loadjava -user internal/internalpasswd -synonym -resolve -verbose mail.jar
Also, the activation.jar and mail.jar files come with some of the files compressed. You must unpack and repack the files without compression:
jar xvf activation.jar; rm activation.jar jar cf0 activation.jar META-INF javax com rm -rf META-INF javax com jar xvf mail.jar; rm mail.jar jar cf0 mail.jar META-INF javax com rm -rf META-INF javax com

Then load the various Java files in the /webmail/java directory:

loadjava -user dbuser/dbpasswd -resolve -verbose BlobDataSource.java ClobDataSource.java MessageParser.sqlj MessageComposer.sqlj

Make sure you create the PL/SQL bindings in the data model file and create the job which will poll the mail queue.

In 8.1.5, add a resolver spec to the above loadjava statement:
-resolver "((* dbuser) (* public) (* -))"

To test that you are receiving mail properly, send a message to user@full_domain_name. A new file should immediately be created in /home/nsadmin/qmail/queue/new. If one does not appear, check out the qmail error logs (usually /var/log/qmail/current) to see what the problem might be. If you have started the polling job, the file should disappear in less than a minute, and the message should be waiting in the user's INBOX.

Reading Email

The web interface should be self-explanatory and documented with Help links. The IMAP interface isn't yet written, so there is no documentation for it.

Last modified: Wed Mar 1 05:16:54 EST 2000 Add a comment | Add a link