I just can’t find a decent email client that looks like it’s from the last 20 years. Geary and Evolution both appear to be pretty modern but something about using Gmail with a Yubikey just doesn’t work and neither of them will connect to my account. Both on Fedora and OpenSUSE. Thunderbird works but it’s so old fashioned and Betterbird doesn’t look much better. What’s everyone else using?
It lets you have all of your emails offline as well. If you have to reference an older email, it’s faster than loading the webpage again.
Some desktop email clients lets you manage your emails, contacts, tasks, and calendars all in one program, which loads immediately instead of loading multiple web pages. This is why I love Evolution and Thunderbird.
If you have multiple email accounts, it’s easier to use an email client, rather than having to log into multiple websites.
The search function in some web interfaces suck.
Some people just don’t like their email provider’s web interface.