When comparing Opera Mail vs Mailspring, the Slant community recommends Opera Mail for most people. In the question“What are the best e-mail clients for macOS?” Opera Mail is ranked 7th while Mailspring is ranked 11th.
Ranked in these QuestionsQuestion Ranking
Pro Opera Mail CAN BE set as default email client in Windows 8 & 10
Pro Automagic smart filtering
After a bit of use Opera learns what e-mail belongs in what folder just by previous usage. This makes for a convenient way to have e-mails filtered without having to manually mange every e-mail.
Pro Free and based on Mozilla code
Opera Mail is completely free to download and use and it is based on Mozilla's code, which is what makes it a bit similar to Thunderbird in looks and function.
Pro Intuitive user interface
The design of the UI in Opera Mail is clean and intuitive, making for an easy to use client.
Pro CPU / battery efficient
Mailspring uses a C++ sync engine designed to be as efficient as possible, so you can leave the app running and not see your laptop battery life drain away.
Pro Unified inbox
Using a single inbox for all of your email accounts helps you get more done in less time. Mailspring supports every major mail provider—Gmail, iCloud, Office 365, Outlook.com, Yahoo!, and IMAP/SMTP—so you have a single, streamlined command center for all your messages.
Pro Snoozing support
You can swipe to archive / snooze messages and specify when you'd like them to resurface in your inbox.
Pro Read receipts and link tracking
Activity tracking is built into Mailspring so you get notified as soon as contacts read your messages and can follow up appropriately.
Con Very limited feature set
Compared to Thunderbird.
Con Does not support 4K monitors
Con Sync is slow
Opera tends to be slower on e-mail sync when compared to other popular clients.
Con No portable windows (.zip) bundle available
Con Pro subscription model
To use some features, like contact profiles and link tracking more than a few times a month, you need to pay for a Pro subscription.