When comparing Mailplane 3 vs Postbox, the Slant community recommends Postbox for most people. In the question“What are the best e-mail clients for macOS?” Postbox is ranked 8th while Mailplane 3 is ranked 18th.
Specs
Ranked in these QuestionsQuestion Ranking
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 Clear interface
Pro Forgotten attachment reminders by default
Reminding the user that they forgot to attach the file if they mentioned one in the body of the email is one of the most useful features of any email client and so many don't include this. Postbox is pre-configured to look for certain keywords (attached, CV, spreadsheet, pdf etc) and you can specify your own keywords in addition.
Pro Blocks tracking gifs
Has the ability to block tracking gifs commonly used for read receipts.
Pro One Inbox for all accounts
All messages in one place. But you can select to show only messages from each account either.
Pro Quick Bar for macros
Quick bar allows you to add a variety of content to your message. It will let you reuse URLS in your Sent folder, and autocompletes against canned responses, signatures, and topics.
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 No support forum
Support for paid product has no online forums.