What are some alternatives?
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
CleanEmail - CleanEmail is an online service that empowers you to take control of your mailbox.
MailClark - The Slack bot for external communications
Email Signature Rescue - Create, manage and deploy beautiful customized HTML signatures in any email client.
DuoCircle - DuoCircle provides enterprise spam filtering and email management solutions.
MessageOne - MessageOne offers email management solutions such as EMS and AlertFind for archiving, e-discovery, security and notification services.