Zope sendmail
Project description
zope.sendmail is a package for email sending from Zope 3 applications. Email sending from Zope 3 applications works as follows:
A Zope 3 application locates a mail delivery utility (IMailDelivery) and feeds a message to it. It gets back a unique message ID so it can keep track of the message by subscribing to IMailEvent events.
The utility registers with the transaction system to make sure the message is only sent when the transaction commits successfully. (Among other things this avoids duplicate messages on ConflictErrors.)
If the delivery utility is a IQueuedMailDelivery, it puts the message into a queue (a Maildir mailbox in the file system). A separate process or thread (IMailQueueProcessor) watches the queue and delivers messages asynchronously. Since the queue is located in the file system, it survives Zope restarts or crashes and the mail is not lost. The queue processor can implement batching to keep the server load low.
If the delivery utility is a IDirectMailDelivery, it delivers messages synchronously during the transaction commit. This is not a very good idea, as it makes the user wait. Note that transaction commits must not fail, but that is not a problem, because mail delivery problems dispatch an event instead of raising an exception.
However, there is a problem – sending events causes unknown code to be executed during the transaction commit phase. There should be a way to start a new transaction for event processing after this one is commited.
An IMailQueueProcessor or IDirectMailDelivery actually delivers the messages by using a mailer (IMailer) component that encapsulates the delivery process. There currently is only one mailer:
ISMTPMailer sends all messages to a relay host using SMTP.
If mail delivery succeeds, an IMailSentEvent is dispatched by the mailer. If mail delivery fails, no exceptions are raised, but an IMailErrorEvent is dispatched by the mailer.
Changes
3.5.0a1 (2007-10-23)
QueueProcessorThread now accepts an optional parameter ‘interval’ for defining how often to processes the mail queue (default is 3 second)
Several QueueProcessorThreads (either in the same process, or multiple processes) can now deliver messages from a single maildir without duplicates being sent.
3.4.0 (2007-08-20)
No changes since 3.4.0a1.
3.4.0a1 (2007-04-22)
Initial release as a separate project, corresponds to zope.sendmail from Zope 3.4.0a1.
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