When you cleanup your trash you get this text

"No conversations in the Trash. Who needs to delete when you have over 2000 MB of storage?!"

I know 6 GB is considered above 2000 MB, but shouldn't you change that :)

Also on the more page in German:
"2,8 GB Speicher und weniger Spam – gratis"
"2,8 GB Storage and less spam -free"