Please help me out!!!!!!!!!!

I get this error message whenever I click on the save button, forward button, or Approve button.

" The operation cannot be completed, probably due to the following:
- deletion: you may be trying to delete a record while other records still reference it
- creation/update: a mandatory field is not correctly set

[object with reference: ir_mail_server - ir.mail.server] "

I believe the error comes because those buttons trigger mail notification action.

After deleting the existing outgoing server, I create a new one but I get this error when I click on "Test Connection"

" Connection Test Failed! Here is what we got instead:
-2
Name or service not known "

Please help me out!!!!!!