I have setup my Murena email account to work with Microsoft Outlook email client 2019 on Windows 10.
When I send email from the client I get the attached certificate error message.
you probably configured “murena.io” as smtp out? then just go for “mail.ecloud.global”
(murena.io points MX to mail.ecloud.global, the initial domain the /e/ services ran with. The certificate only covers the .global domains. Maybe open a ticket with helpdesk for them to extend the certificate)