If you are subscribed to a mailing list which is treated as spam by mistake, you can exclude its address from filtering by clicking Not spam! on the page when reading messages. The address will be whitelisted and new messages from the mailing list will go to the Inbox.
You can edit your whitelist at any time in Settings → Mail processing rules. To add an address to the whitelist, fill in the field and click Add. To remove an address from the whitelist, select it and click delete from list.