Net::SMTPAuthenticationError with use of gmail smtp

Before today my mail service is working well. But i got suddenly Error
for Net::SMTPAuthenticationError

And get error page with following message

421 4.7.0 Temporary System Problem. Try again later (HS).

can any one help me in this? Why this occur? I haven’t do any changes in
my settings. Its same as before my mail service is working… Is there
any service issue?

Chirag Shah
Software Engineer