Siteground Email - How to configure?
There few CiviCRM extension that use third party to send bulk emails or transactional emails.


FlexMailer
Sparkpost
Mandrill


Alternatively there are many SMTP providers that provides good bulk mailing service like Sendgrid, CiviSMTP etc. Here is the list of SMTP providers that CiviCRM bulk mailings are supported.

HTH

Pradeep