Mail solution - Recommendations

Hi all,
I am looking for some advice on the choice of the most suitable email application. I am running a small business with 6-emails (inboxes) that are having personalised domains: @domain-name.com.
As of today, my email hosting services are at OVH and I use Roundcube. I am rather limited with Roundcube and I would like to move to a better mail solution/ app.

My requirements for that would be as follow:
- with great/modern UI / interface, customizable in look and feel, colour
- intuitive, easy to use
- good speed/performance
- can manage all inboxes in one place, including emails and folders access (6 different email/inboxes)
- search in all folders
- can do a mass email to multiple with personalised content
- calendar management
- snooze emails notifications, attachment reminder
- browser version, desktop application with compatibility: Windows, Mac
- mobile application available for iOS, Android
- free/open source
- secure
- analytics

Would you have any recommendations for that? I am currently exploring both Thunderbird and Proton.

Many thanks.
Best

Pierre

Rather than an installed E-Mail Client like Thunderbird, Microsoft Outlook, EM Classic, etc., does your Domain hosting service provide Webmail and how many accounts? [Mine does with 2 addresses, called SmarterMail.] An advantage to Webmail is it can be accessed from any computer using any Web Browser. Most ISPs provide E-Mail but may be limited in how many accounts. Might give the SeaMonkey browser a look-see, includes an E-Mail Client. There was also the old Hotmail.com and supposedly successor Outlook.com which have both merged into Outlook – free personal email and calendar from Microsoft.

Hi Berton,

Thanks for your answer and help. My domain hosting service is providing 10 emails.
With them, the email client I can access is Roundcube - Roundcube - Free and Open Source Webmail Software
which isn't that great, a bit outdated and doesn't support all the requirements I have.

I am using Outlook.com for personal usage, great one to be fair but I can't use it for professional.

Any other advise besides Thunderbird, Proton or SeaMonkey?

Maybe more here:

eM Client looks quite good I will explore this one further. Only concern here seems to be the pricing.