530 5.7.0 Must issue a STARTTLS command first

[rudracomputech]

First of all thankyou for creating such a great tool. We installed it on our server and getting below error while sending the email

Fatal error: Uncaught exception 'Swift_BadResponseException' with message 'Expected response code(s) [250] but got response [530 5.7.0 Must issue a STARTTLS command first]' in xxx/xxx/xxx//httpdocs/modules/swift_mailer/php5/Swift.php:250 Stack trace: #0 
xxx/xxx/xxx//httpdocs/modules/swift_mailer/php5/Swift.php(310): Swift->assertCorrectResponse(Object(Swift_Events_ResponseEvent), 250) #1 

xxx/xxx/xxx//httpdocs/modules/swift_mailer/php5/Swift.php(319): Swift->command('RSET', 250) #2 
xxx/xxx/xxx//httpdocs/modules/swift_mailer/php5/Swift/Authenticator/LOGIN.php(36): Swift->reset() #3 
xxx/xxx/xxx//httpdocs/modules/swift_mailer/php5/Swift/Connection/SMTP.php(407): Swift_Authenticator_LOGIN->isAuthenticated('xxx', 'xxxx', Object(Swift)) #4 
xxx/xxx/xxx//httpdocs/modules/swift_mailer/php5/Swift/Conne in xxx/xxx/xxx//httpdocs/modules/swift_mailer/php5/Swift.php on line 250