You should be able to see database size from the Administrator console. But “full” is a relative term. Do you have a quota on your mailfiles? Do you have warnings to the users?
If I’m being too simplistic here, I apologize. I don’t know your level of Notes knowledge or experience.
In Notes 4.x, the mailfile locked up at 1 to 4 GB, depending on what was set when the mailfile was created (I believe the default was 1 GB, an enormous amount of space at the time). I know in 6.x, there is no limit, so “full” is only what your company decides to define it as.
Remember that in Lotus Notes, the % shown in the properties is the % of mailfile that is not empty space. If you have a 100 MB mailfile but it’s only showing 20%, that doesn’t mean the user has 80% available. It means that 80% of that mailfile is empty space. Compacting the mailfile gives you it’s TRUE size, around 20 MB and something over 98%, which means that 20 MB is real data, not empty space.
So you may have a limit which you have set by policy or at creation, but other than that, the only limit on a Notes mailfile is how much you, as the administrator, are willing to put up with.