Solved the problem by using SMTPS with port 465.
Commons Email doesn't seem to handle SSL well, since isSSL always appears as false in debug mode. So I overrided the send method from HtmlEmail:
@Override
public String send() throws EmailException
{
buildMimeMessage();
// Implementação padrão de send() não conecta corretamente via SSL
Transport transport = null;
try
{
message.saveChanges();
transport = getMailSession().getTransport("smtps");
transport.connect("email-smtp.us-east-1.amazonaws.com", 465, <<amazon SMTP username>>, <<amazon SMTP pasword>>);
transport.sendMessage(message, message.getAllRecipients());
return message.getMessageID();
}
catch(MessagingException e)
{
throw new EmailException(e);
}
finally
{
if(transport != null)
{
try
{
transport.close();
}
catch(MessagingException e)
{
throw new EmailException(e);
}
}
}
}