For the lazy (like me), here's a link to the Geary GNOME page and here's a screenshot (bah, top-posting!). Note to Yorba/GNOME: you guys need a screenshot gallery somewhere for your software.
Geary just had a new release (40.0) that is supposed to be friendly for smaller screens. I haven't tried it myself, but it's available as a flatpak on flathub.
https://wiki.gnome.org/Apps/Geary (keep in mind that the version in your distro's package manager may not be 40.0 yet, which is why I mentioned the flatpak)
Mozilla has stopped the active development on Thunderbird, however, the dev community still exists and Thunderbird is actively developed (maybe at a slower pace than before), and security issues are regularly fixed. I really don't think one should conceive Thunderbird as insecure.
I personally use Evolution which is maintained by the Gnome team. It is aimed at more business-oriented users (at least that's what Gnome claims) and I am very happy with its good Exchange functionality and its overall professionalism (including GPG and S/MIME encryption out of the box, excellent filter rules and more). A very elegant, yet not power-user oriented alternative is Geary, also maintained by Gnome. If you're more old-school, have a look at Claws, too.
If you prefer Qt, KMail might be for you. It is very feature-rich, but I find a bit cumbersome to use (which is in line with a lot of KDE applications, imho). A light-weight but powerful alternative is Trojita. It is certainly worth a look.
You could try switching between the flatpak vs deb version of geary, or even the nightly flatpak version of geary, found here:
https://wiki.gnome.org/Apps/Geary/GetIt
If you are still having issues, You might be able to get more help if you post to Geary's issues in gitlab:
https://gitlab.gnome.org/GNOME/geary/-/issues?scope=all&state=opened
Take a look at open issues first before posting to see if the issue already exists (I didn't spot it, but that doesn't mean it isn't there). And looking at them can help you understand the level of detail you need to provide in order to get help.
Consider putting this issue on Geary GNOME Page or on Pop_OS! Issues.
I noticed that if the Internet connectivity is not at its best Geary behaves a bit off.
Looking at Geary's page here;
https://wiki.gnome.org/Apps/Geary/Donate
> Support for developers
> Geary is primarily a volunteer-based project. While we occasionally receive code contributions from people paid by companies to do so, the great majority of work is carried out by people volunteering their time. As such, any financial support you provide will directly benefit developers, translators and others and allow them to devote more time to making Geary great.
> No developers are currently available for support.
However looking at https://gitlab.gnome.org/GNOME/geary/
I can see there is active development going on.
Maybe you can file a bug report or see if there is a discord channel or something that they are using for development and ask them there to populate the Developer support table or ask them were they would like donations on specific bugs posted.
If it is indeed just your email client causing issues and Mutt isn't your cup of tea, (Geary)[https://wiki.gnome.org/Apps/Geary] may be to your liking.
It has quite a nice simple interface, and I believe that these days they also have some sort of affiliation with the Gnome project
As for DE suggestions, my own preference would be Xfce if Gnome isn't working out as that can still operate somewhat simlarly compared to other DEs I've tried
> All private email providers seem to be incompatible with standard email applications like outlook
ProtonMail gets around this with ProtonMail Bridge. I run this along with Geary on a Pinephone to manage emails.
I also may suggest a Geary, probably it is the most suitable for your requests.
By the way, I have found a similar layout in Polymail, but this email client for Mac OS. All my friends use Mailbird and it’s a good email client, but this email client for Windows. I hope they will make a version for Linux and Mac soon.
For GUI clients Mailspring looked alright when I tried it, but it's an electron app so I didn't mess around with it for long. I've had people suggest Geary to me, but I've never gotten around to trying it. I'd really rather Thunderbird keep chugging along.
As a mutt user, he's not that guy, he's that man.
While O365 does support actual mail protocols, i.e. IMAP(S), SMTP(+TLS), your environment might use an authentication mechanism which isn't supported by the mail client such as ADFS (of some version or implementation thereof). This will likely leave you using a web browser as a mail client. Both Firefox and Chrom{e,ium} now have access to full functionality, which was not the case until fairly recently.
I'm currently running Chromium 66.0.3359.181 and Firefox Quantum 60.0.1 on Fedora 27 with no problems (not counting handling the fonts). Back when Fedora 25 was current I was unable to get Thunderbird - including with Exquilla, Evolution with EWS or geary* to work with the local authentication.
*[Just kidding. I didn't bother trying geary.]
I've got the same problem, but I'm unable to update geary 0.8.3. I've tried all those instructions like this one here http://www.omgubuntu.co.uk/2015/03/install-geary-ubuntu-linux-email-update, and I've downloaded tar.xz from here https://wiki.gnome.org/Apps/Geary . Nothing works, it's still geary 0.8.3. My system is OS Freya
It has less to do with the style of buttons / widgets and more to do with the placement / number of those elements, and how they define workflow.
Of course one of the beauties of Mozilla products has always been extreme customization, but the default leands towards more extraneous things in Thunderbird that nobody uses. My personal feeling would lean toward a more minimal interface -- I think Geary does a good job with this (insomuch as it's become my de facto mail client), but I'd love to have such a thing incorporated with the power and flexibility that Thunderbird provides.