Afteroffice has already filtered off a lot of junk mail at server level. Those that bearing lower junk sensitivity level will be let through for individual users to set their own filtering options.

Individual users may go to their Profile > Statistic to see the composition of their incoming mail and the percentage of junk mail filtered by our servers. This feature only available for our Webmail Pro and Virtual Office subscribers.

Those email that published on your website are bound to receive more junk as they are easily pick up by spammers.

To ease the pain, you may setup the junk filtering options on your webmail.
Please follow the steps here: To enable junk mail option.

If you are using mainly POP and do not login to webmail often to delete your junk mail collected in the Junk mailbox, you can setup your mail client to download the junk mail from time to time.
Refer to the steps in: Getting Email From Junk Mailbox.

*You can enable the automatic Junk mail purging process also by login with the administrator account (usually avomaster), and enable the Junk mail auto-delete option under Profile.