The sender address if the email address people see your newsletter is coming from.
You should consider two aspects: the technical one and the user experience.
From a technical point of view, the sender address can be part of the spam rank or checked by your provider before start the mail delivery process. The best choice is to use an address of your blog domain, for example firstname.lastname@example.org.
That address should be a real mailbox or at least an existent alias of a real mailbox. And it should be checked for replies (sometime people reply to newsletters) and for error messages.
From a user experience point of view, receiving an email from email@example.com is clearer than firstname.lastname@example.org (many business register an official email address on a free service like gmail: this is ok to run your business and register accounts, but not for communicate with your customers).
Actually, setting the sender with a free service domain won’t work, your newsletter will be mostly rejected (you’re not authorized to send as @gmail.com from your server, only Google can).
Blogs sometimes live in subdomains, like sport.yourdomain.com. But the mail service refers to the official domain name (yourdomain.com) which identify your company or your brand. A subdomain is usually activated for specific services, like a shop or a forum.
We suggest to not bind the sender to a subdomain, like email@example.com, but to use the standard domain maybe differentiating the “local part”: firstname.lastname@example.org. That practice leave you the freedom to dismiss the subdomain without loose the connected mailbox.
Always ask your provider to setup thre SPF record in the DNS to set the server hosting you blog as an authorized server to send email for your domain. And, if possible, use the provider mail service to send newsletter.