Sparkpost - Deliver your app and website emails on time and to the inbox. Trusted to send 25% of the world's non-spam email. Email delivery for companies big and small.
EmailPlayground - EmailPlayground provides solution to schedule and send emails with ease.
SocketLabs - Marketing & transactional email delivery platform
SendLater - Email scheduler for Mac Mail.
Return Path - Inbox placement solutions from Return Path helps improve email deliverability and increases email marketing ROI.
RGB Technologies - Email Scheduler - Email Scheduler provides an intuitive email scheduling solution, integrated within the existing Salesforce account.