I recently had to help a client move e-mails between two accounts and thunderbird out-timed multiple times. After finding out that not our firewall or the account is the issue (two gmail accounts) I looked and found some report on the mozilla forum about the issue. The workaround was to copy it first locally and then move a certain amount of emails manually.
Also I prefer the UI over current Thunderbird but I think this design could win me over:

But it seemingly needs to be configured manually to achieve that look reddit link?
Not really in the mood for trying that out.
I also need to mention I make heavy use of my personal domain and have several email accounts. It’s already a pain to manage them on the phone but sadly even there the option is gmail or outlook. Didnt look too much into alternatives but I am cagey about others having access to my SMTP password.
Yes, I heard that Microsoft attempted to hijack the (new) Mail app on Windows11 to MS news but I (hope) that they don’t do that with their Outlook Android/Windows version and only with their native Win11 client

I don’t use outlook anymore but I do use Thunderbird and the UI is janky and outdated, plus it has to download and catch up on messages every time you open it.

You are entitled to your own opinion but so am I.
This opinion is purely from a usability standpoint. I like the office suite and prefer the editing and menu over open/libre office.
And I say this as someone that created letter templates for clients.
Creating forms is way easier on Writer though. Very good (free) way to create forms!

It is, but not enough to move the needle. It also carries a bunch of bloat.

I also use Roundcube with several plugins/add-ons.