[Zope 2.12.0] Mailhost thread should be started upon startup

[Andreas Jung]

Right now the Mailhost thread (for asynchronous mail delivery) is checked/started when sending a new mail.

I would be much smarter to register an event subscriber for IProcessingEvent or IDatabaseOpened in order to start the thread
directly while starting Zope (e.g. for processing remaining entries in the mail queue). However this can be tricky since there might be multiple MailHost instances spread across the ZODB object hierarchy

[Colin Watson (cjwatson)]

The zope2 project on Launchpad has been archived at the request of the Zope developers (see https://answers.launchpad.net/launchpad/+question/683589 and https://answers.launchpad.net/launchpad/+question/685285). If this bug is still relevant, please refile it at https://github.com/zopefoundation/zope2.