Hi.
I am not sure if this kind os post is allowed, if not delete it without problem, but we are working in a project that can interest to the libreoffice community.
We are 3 spanish engineers that have started a open source project for cover this gap.
After try em client, spring mail, thunderbird and others we think that today, and alternative to outlook not exists.
We usually use open source projects on our desktop, but for us, find an alternative that beat outlook are impossible today. We want create a complete open source alternative, in fact we have started, but we realized that is much effort for a hobby. We have decide created a kickstarter project to allow us live, for a year finishing the project. If you want know more, you can follow this link:
https://www.kickstarter.com/projects/1692742944/mailer
Our goal is finalise the project and publish as open source complete email, contacts and calendar alternative, integrated with jitsi for chat and video conference.