My thoughts were:
In Outlook/Thunderbird, there is a plugin, that puts a button in the toolbar: Save to OpenPetra.
When you click this button, the plugin connects to a webservice of OpenPetra (eg openpetraorg.sourceforge.net/dbd ... p=mailroom).
There needs to be permissions who can see those emails, but it should be possible for other users with the same permissions, to see the email correspondence with that partner.
The contacts (and emails) have to be searchable within OpenPetra. Christian prepared a prototype for improved contact management several years ago.
In OpenPetra, we should have a button for "Send Email" on the Partner Edit screen, which will open the default email client with the correct Email Address.
The plugin for Outlook/Thunderbird should have a second send button, which will send and save the email to OpenPetra again.
I don't know if there are better solutions to this (perhaps even implementing a simple IMAP client within OpenPetra), but this is my proposal, open for discussion. Best if we had some user feedback on this as well, especially people on the iConnect project, because BBES also has Outlook integration.