Clean Email - Clean Email is an online service that empowers you to take control of your mailbox.
Spamihilator - The free Anti-Spam-Filter Spamihilator removes more than 98% of spam mails before they even get into your inbox.
MailClark - The Slack bot for external communications
SpamAssassin - Use this program to "Unspam" your mailbox(es).
Hiver - Manage Customer Support, Sales and Projects right from your Gmail inbox. Collaborate with Shared Labels, Shared Contacts, email notes, email reminders and email templates
Spam Reader - Spam Reader is a free anti-spam add-on for Microsoft Outlook.