Respondable

Respondable is part of Boomerang for Gmail and scores your email as you write it, predicting how likely it is to get a reply. It explains the factors behind the score, such as tone, politeness and subjectivity, and suggests changes.

Boomerang trained the feature on data from millions of messages, combining several machine learning techniques to find what affects response rates. Advice appears alongside the draft in real time, which helps with outreach to clients, hires or partners and with tricky emails to a manager.

It comes bundled with the Boomerang extension, which also handles send later, email reminders, read receipts, follow-ups and meeting scheduling inside Gmail. Boomerang offers a free tier with limited message credits and paid plans with unlimited credits.