Lots of questions... Not many simple answers, but some things to think about:

The community integration is basically an extra recipient source in an assembly. It is available for Mail 5.0 as well, but I don't know why it isn't installed. If you install a Relate site it will install CMS 6, Community 4 and Mail 5, including this extra assembly. Maybe you could just copy it from such an installation?

Your Community site, is it a standalone Community site (no EPiServer CMS in the application)? I don't even know if you can do that anymore, but I thought I'd ask since you say the other sites are CMS sites. Generally if sites don't show up when installing something in deployment center it means that the versions are not compaitble. But since you got it working anyway I don't know...

Are you a member of the Administrators group in the EPiServerCommon role provider? Your SQL/AD groups won't matter (unless you have the CommonIntegration provider/module). EPiServer Mail, just like Community, uses its own system of users and groups (roles). I think the Administrator role in this provider should get access to Mail, but you can also try to add MailAdmins and MailEditors to your user since those are the default groups with access to the Mail features. These groups should have been created by the install. If not, it might be tricky because you have to set the ModuleAccessRights for the Mail module to the group you create, and there's no UI for doing this...

Any case you accidently created a second Common database when installing Mail, rather than installing it in the same database as your Community install? Because if you did you now probably have two sets of user accounts and groups and your role provider can only be connected to one database (I think).

The test licenses seem to act as production licenses, yes. I think test licenses are what the test department here use, and they popped into active mode just like a production licence (the activation mail said "thank you for installing a production license" though, so maybe we actually have production licenses there?).

Ok, I wasn't clear in my statement when I wrote Community site. Of course it's a CMS with Community added to it. What I meant was that the sites I got in the list was basic CMS sites, not the ones with Community added to them.

No second Common database created. In the development site I use only one database for the CMS and Community, but I smartend up when I did the setup for test and production. 

Based on your answers it seems like I have to go back to the role provider and look at its setup, but what I remember from setting up the CommonIntegration provider is that it was a bit of a hassle. I had to struggle to get the wanted SSO the customer wants since the site is an intranet working against an AD.

Then maybe the problem is this simple: Your role integration etc works, but the default Mail permissions don't allow access for Administrators but only for MailAdmins and MailEditors. Does the Mail module show up if you go to module access rights in community admin?

I can only see a WebMail module there, but I think that one has been there since the beginning.

Added to MailAdmins and MailEditors to my Community user and now it works... Not the smoothest way, but wth... =)

Thanks for pointing me in the right direction!