Recent changes to email providers' (notably AOL and Yahoo!) policies to prevent SPAM impact the delivery of mail if you use a non-business email account. If you are using an email address like "email@example.com" or "firstname.lastname@example.org" as your primary email in CORE and attempt to send email marketing, you will see a high bounce rate.
Yahoo! and AOL changed how they use Domain-based Message Authentication, Reporting and Conformance (DMARC) validation. Basically, if your From address doesn’t match the sender address from the mail server, Yahoo!, AOL, or other ISPs will flag email as fraudulent, or as SPAM, and block it from their systems.
To avoid this issue, don't use email addresses from AOL or Yahoo! for your business and your email marketing efforts.