See the following thread on OVH server login problems that eg: needed “plain text login strings” in the account diagnostic tab in eM Client V10 due to the server older authentication methods.
So this might also be why you are also getting invalid username and password and fix that.
So, if emclient cannot connect to ovh exchange servers, i will buy another software
If the above OVH posts don’t help you by putting in the plain text login strings in the diagnostic tabs, then suggest next if you have a current active paid Pro or Personal or Business version, then go to the VIP Support Page and login with your registered email address and password and lodge a support ticket for further official assistance.