What are some alternatives?
CleanEmail - CleanEmail is an online service that empowers you to take control of your mailbox.
Astro - The ASTRO Command Center software is specifically intended for use with: MixAmp Pro TR (late 2015 release), A50 Gen 3 with Base Stations (late 2016 release), A20 Wireless (late 2017 release).
Dimelo Mail - Dimelo Mail is a software that manage inbound emails.
WP Mailster - WP Mailster enables you to run a listserv-like email discussion list on your WordPress site.
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
Vade Secure - Email security to protect against email-borne phishing, spear phishing, malware, and ransomware. Email security and management based on artificial intelligence.