Private smtp server

Help
1

Hi,
I have a private smtp server. I am getting “The remote certificate is invalid according to the validation procedure”
I tried many post from the forum but no success.
I used The remote certificate is invalid according to the validation procedure (error from Robot )- Troubleshoot steps but not able to remove the error.
Can anyone tell me is there any server setting which must be done in order to deal with this error.