SwiftTransport Exception : Expected response code 220 but got code "421"

Question

I am using FOSUserBundle with Symfony2 , a few days ago the sign up processes works fine, then suddenly I get the folowing error when signing up :

Expected response code 220 but got code "421", with message "421 Cannot connect to SMTP server x.x.x.x (x.x.x.x), connect error 10061
 500 Internal Server Error - Swift_TransportException
"

with :

x.x.x.x stands for smtp IP adress

It's related to smtp. Any idea how to solve this problem ?

Answer 1

as @cheesemacfly said it was a problem of my smtp server. it was down.

I waited for a while reattempted an it worked fine.