Most people start out with plain old SMTP I.e. Gmail, Google Apps (paid email: custom domain), Hotmail, or any other provider.
But the thing you have to keep in mind here is that these providers are used for what is colloquially known as "transactional email". Transactional emails are the, what the average user perceives as, regular emails. Think order confirmation emails, "Hey, Did You Know About This?" emails, and so on. Sending mass mailings via these services is most of the time heavily frowned upon and you run the risk of not only hitting the send limit per day quickly but in the worst event having your account disabled.
From what I gather is that you're interested in sending a large number of emails in a short period of time. The classical email blast, so to say. And for this, you will need either your own mail server. I.e. Exim, Postfix, or if you're really serious PowerMTA, all examples of Mail Transfer Agents (MTA's.) Or you could opt-in to use a service that allows mass emailing and is available in the MailWizz interface (Servers -> Delivery Servers.)
One trick that you could implement is to look at companies that offer a free monthly tier, sign up on as much of them as possible, look at the quota's and have MailWizz switch from Y to Z after X amount of emails. This could allow you to send as many emails as possible for almost next to nothing.
And thanks for the compliment, but I think that is a bit to much honor. I wouldn't dare to call myself a pro when it comes to email.
And
is considered a security risk in shared hosting environments. When Siteground warns you about this being a security risk it probably means that the PHP is running directly with permissions of the Apache web server and not with permissions of the user. My guess (and hope) is that Siteground runs either php_fpm or FastCGI, so this wouldn't really be an excuse, but you would need to contact Siteground to get an idea about this.
Hope that helps.
