PigeonBot - Send emails via Slack with the /email command
TextBlast Bulk SMS - Send personalized mass messages easily
Inbox Ignite - Prevent your emails from going into spam
Porterhouse - Send mass iMessage and SMS texts from your existing number with a single click!
Thunder Mail - Cheap and simple transactional emails API with Amazon SES
LoopMessage - LoopMessage is a perfect macOS tool for personalized mass messaging via iMessage/SMS, WhatsApp, Facebook Messenger, Telegram, Viber, and Skype.