I have problems with my Groupwise email account when I use Thunderbird or Mail application (on Mac).
I can receive emails with no trouble but when I want to send an email from Mail or Thunderbird, I get:

Cannot send message using the server smtp.groupwise.***.***
Verify that you have addressed this message correctly. Check your SMTP server settings in Mail preferences and verify any advanced settings with your system administrator.

Select a different outgoing mail server from the list below or click Try Later to leave the message in your Outbox until it can be sent."

The port is the one recommended by the IT services of my company, and even if I try with other suggested ports, it fails. The other parameters (username, SSL..) are set correctly.

It does fail on both Mail app and Thunderbird...

Thus, does anyone know why it does so, and how I could solve the issue please?

Thanks !