It works better for searching, it works offline, catch-all addresses just work with correct from address when replying, backup and archiving, can move mails from box to box without sending.
I also use roundcube, but only to read mails. If I want to reply to a catch-all mail I have to create an alias which is super tedious.
I have email addresses under Outlook (old personal account), Gmail (study provided email), Exchange (work) and Proton (main personal account). I also actively use the calendar feature in my client, which is sync'd up to my Nextcloud instance.
Just having it all under Thunderbird is so convenient and it feels more private. It's also an entirely consistent UI between accounts
Same reason anyone would use a dedicated provider-independent client instead of a proprietary web application locked into a single provider: less vendor lock-in, more local control, and so on.
Replaced with one god awful one. I actually liked the calendar application, does all I need it to do. But no, I can't have just a calendar application anymore according to Microsoft
Mozilla used to have Sunbird, until they also rolled it into Thunderbird. Standalone calendars aren't popular anymore, but in sure there's some around.
I understand the mail integration, as appointments can be processed directly.
They haven’t turned them on just yet owing to a little last-minute work, but your ability to sync calendars and address books with an ActiveSync/Exchange-compatible eMail server is coming soon.
If anyone's in this thread because they're looking for a new mail client after Microsoft killed the old Mail app, and haven't been happy with the typical suggestions of using each email service's web interface or Thunderbird, I found I don't hate Mailspring (with the fancy features disabled - I just want my email client to do email well and don't want extras that provide clutter).
New Outlook is a pile of shit compared to the desktop Outlook app. It's been causing a lot of headaches for my coworkers. Microsoft had better port near every single feature over to the newapp before they force everyone on it.
The majority of regular folks will only ever upgrade when they get a new computer. Most Me Maw's and Pa Paw's would sooner let their computers catch fire from being loaded with cat than get a new one. Hell. They are all still using ball mice.
As for me, as long as I have an iso I'll happily run it in a vm. Indefinitely.
The new outlook is utter garbage. It was in fact so bad that I uninstalled it and now use it through the web front-end only. And I'm doing that in Edge - as the only website this browser is allowed to open (asides from Teams, where the software is just as terrible).
If they call it a success that no more people are complaining because they just gave up, then, congrats... I guess?
I absolutely dislike Outlook desktop, don't trust it either. Used Thunderbird back in the day, but switched to emailing on tablets or phone + TrueNas for desktop files.
FairEmail Pro on tablet is all I need for email. It is open source and imo simplest to use. It's free and the pro version set me back 7€ or so.