title: What to do when external service to validate data fails?
body: <p>Let's say we have a system that needs to validate data using a third party system. For example, we allow user registration and we validate the provided email address using an external system that tell us if the email is valid, if it is a temporary email etc, etc.</p>
  
  <p>Our system receives the email address, makes a request in real time to the third party email validation system and, depending on the response (email valid or not) it will allow the user to register.</p>
  
  <p>My question is: What happens if something goes wrong with the connection? (timeout, DNS errors, etc). I think it will be wrong to allow the user to continue the registration process because we don't know if the email is valid but, at the same time, we can't stop the registration process because the email might be valid.</p>
  
  <p>I'm thinking in trying the connection more than once (let's say, three times). If it fails, then return an error code with a message like "Please try again later". Is this the right approach to this problem?</p>
  
  <p>Thanks in advance :D</p>