When comparing Mailplane 3 vs Newton, the Slant community recommends Newton for most people. In the question“What are the best e-mail clients for macOS?” Newton is ranked 14th while Mailplane 3 is ranked 18th. The most important reason people chose Newton is:
Newton grabs information from LinkedIn, Facebook, and Twitter accounts linked to the sender's email address. It then displays information which can help you figure out who the emailer is, such as their job title and where they work.
Specs
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Pros
Pro Can work with mutiple Gmail accounts simultaneously
The tabbed interface included in Mailplane 3 lets users work with as many Gmail accounts simultaneously as they want.
Pro Fast and light
Pro Doubles as a calendar
Mailplane 3 combines Google Calendar and Gmail within a single app.
Pro Easy to use
Mailplane 3 looks just like Gmail's web UI and even imports Gmail shortcuts. If Gmail shortcuts aren't ideal for the user, those of Mac can be used instead.
Pro Supports many plugins
Functionality and features can be extended by using plugins.
Pro Know who's emailing you
Newton grabs information from LinkedIn, Facebook, and Twitter accounts linked to the sender's email address. It then displays information which can help you figure out who the emailer is, such as their job title and where they work.
Pro Snooze incoming emails
You can snooze emails to come back at a convenient time - whether it be in 2 hours, or next Wednesday.
Pro Works across multiple platforms
While there is no Windows app, Newton is available on iOS, Android, and macOS, including Android Wear and Apple Watch.
Pro Logs messages to Salesforce
Pro Had everything you can dream of
Cons
Con Written for those who drink Google's Kool-Aid
It's a thinly-veiled skin over the browser interface. Why bother?
Con Can freeze very often
Con Gmail only
Mailplane 3 is a Gmail-only client. It does not support other email providers.
Con Subscription based
Newton costs $49.99 per year after the 14 day free trial.
Con It's "stupid expensive"
$49.99/year? Really? And it doesn't cook, clean, or serve beer. There are better email apps for far less money.