Pyramid_exclog : SMTPAuthenticationError: (530, 'Must issue a STARTTLS command first')

I'm using pyramid_exclog to log exceptions and send those exceptions as email. I'm using Amazon aws SMTP to send emails. But I'm getting the following error:

SMTPAuthenticationError: (530, 'Must issue a STARTTLS command first')

Here's the code I use:

[handler_email_exc_handler]
class = handlers.SMTPHandler
args = (('email-smtp.us-east-1.amazonaws.com', 587), 'no-reply@company.com', ['me@company.com'], 'Company Exception' ,('<username>','<user_key>'),None)
level = ERROR
formatter = exc_formatter

As far as I know, there's nothing wrong with the aws credentials, since I used them to send mails via Thunderbird.