When comparing Mozilla Thunderbird vs Geary, the Slant community recommends Mozilla Thunderbird for most people. In the question“What are the best native e-mail clients for Linux?” Mozilla Thunderbird is ranked 1st while Geary is ranked 3rd.
Ranked in these QuestionsQuestion Ranking
Pro Lightning Calendar and Address Book integration
Pro Free (as in freedom and beer)
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 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 Available on Linux, OS X and Windows
Pro Large assortment of plugins available
Mozilla Thunderbird offers a huge amount of extensions to expand the usability and options of the client.
Pro Very reliable
Version after version, Mozilla Thunderbird works as expected.
Pro Tabs for navigation
Pro Straightforward and simple UI
Setting up accounts is a simple as putting in the users e-mail address and password.
Pro Fast and responsive
Geary is faster than most e-mail applications, upon starting the program or even just browsing in folders.
Pro Beautiful UI
Everything about the look and feel of Geary is a breath of fresh air after the clunkiness and ugliness of it's competitors.
Pro Threaded conversations
Threaded conversations means all subsequent replies are view-able underneath the initial e-mail.
Pro Native GNOME application
It looks and works like a GNOME application should, so it Just Works™.
Pro Work in background
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Con Outdated interface
Thunderbird's interface is very outdated and unpleasant. It feels more like a Windows XP application than like a modern MacOS one.
Con Terrible integration with macOS
Simple things - drag/dropping pictures doesn't work, for instance.
Con No horizontal layout
There is no optional horizontal layout for those that want to be able to view their emails headers across the full screen.
Con No PGP
No encryption available.
Con No Pop3 support
Con No images in HTML signatures
Whilst it is possible now to add a HTML or plain text signature per account, there is no support for per images in the signatures. This is a must for when an employer imposes a set signature with images.
Con No native Exchange support
Whilst possible if your Exchange server and account are using Davmail as a proxy, at the moment you can't natively add an Exchange account.
Con Not seen as a secure app by Gmail
Con Made for Gnome 3
It may look out of place in any other desktop environment.
Con No incoming message rules
Con Development is pretty dead
No real development since March 2017.
Con No proxy support
Seems like it can't retrieve email from behind proxy.