When comparing Mail.app vs Mozilla Thunderbird, the Slant community recommends Mozilla Thunderbird for most people. In the question“What are the best e-mail clients for macOS?” Mozilla Thunderbird is ranked 2nd while Mail.app is ranked 4th.
Ranked in these QuestionsQuestion Ranking
Pro Will probably be enough for a sizable chunk of users
Since it's the built-in Mac email client and is quite complete feature-wise, most users will not really need any other third-party applications out there. Mail.app should be enough for their needs.
Pro Easily annotate pictures or sign documents inside the client itself
Mail.app has powerful markup tools which let users add annotations to images or even sign documents they got through email without ever leaving the client.
Pro Integration (with other Apps/Hardware)
One thing Apple does well is to integrate its apps and hardware. The mail app is no exception. If you must be in the hermit kingdom, at least take advantage of the (often excellent) features provided.
Pro Smart folders on steroids
- You can choose out of tenths of mailheaders (several hundreds including virtual headers)
- "<header> is (not) in <folder> <header>" operator which enables you to do cool filters
- Each smart folder can have smart subfolders by an user definable key
Pro Shows threaded view with snippets in middle panel
Pro Can be easily extended
If the basic features inside Mail.app are not enough, it can easily be extended through plugins to add new features.
Pro Free (as in freedom and beer)
Pro Lightning Calendar and Address Book integration
Pro Available on Linux, OS X and Windows
Pro Good filtering system
Mozilla Thunderbird offers a flexible filtering system with the ability to set flags and read/unread, as well as sort/assign to new mail directories. There are also numerous plugins available to assist in the filtering.
Pro Very reliable
Version after version, Mozilla Thunderbird works as expected.
Pro Consistent and involving a moderate learning curve
The app design of Mozilla Thunderbird has not changed significantly since its beginning, making its learning curve almost non-existent.
Pro Large assortment of plugins available
Mozilla Thunderbird offers a huge amount of extensions to expand the usability and options of the client.
Pro Tabs for navigation
Pro Send large files easy
Install pCloud plugin for Thunderbird and your files (upto 20 GB free storage included) will be received as download links
Con Missing lots of advanced features
Out of the box, Mail.app may not have as many features as some other options. This can be mitigated with plugins though. But that is not a perfect solution since third-party plugins may not be very reliable in the long run.
Con Really bad reliability
Database engine gets stuck consuming 100% of one core; crashes; a 40GB log file has been spotted.
Con Updates may break plugins
Apple is known to make API changes to Mail.app when updating which break a lot of plugins.
This can be very annoying for users whose workflow heavily relies on plugins, since they have to wait for plugin developers to make the changes needed to fix any issues brought by the update.
Con No option to snooze emails
You can not snooze emails to view later. This makes it hard to keep the inbox clean at all times since you have to read every email and choose to delete or keep them the moment they arrive to do so.
Con Poor performance for some users on El Capitan
Con Poor calendar integration in exchange mode
Con Terrible integration with macOS
Simple things - drag/dropping pictures doesn't work, for instance.
Con Development slowed to only focus on stability and security
Mozilla Thunderbird has slowed down its development of features to only focus resources on security and stability.
Con Subject lines can (temporarily) disappear from the list
This is sporadic behavior.
Con Serious bugs
Clicking on a subject line can bring up the wrong email.
Con Outdated interface
Thunderbird's interface is very outdated and unpleasant. It feels more like a Windows XP application than like a modern MacOS one.