Large email providers such as (AOL, Gmail, and Yahoo) have implemented tougher policies on who or what can send email on their behalf. A very large portion of unwanted email (SPAM) is forged via email addresses at these large email providers. In order to cut down on these forged attempts, the email providers are instructing other mail servers to reject any message that is sent unless it originates from their servers.
Therefore, Big Biller will not send email on your behalf unless you change your email address to a domain name that you control and has an active email account.
Please note: Integrating your Google account with Big Biller will allow you to send standard mail directly from your Gmail account, rather than from Big Biller’s email servers. Mass emails will continue to be sent from Big Biller’s email servers and therefore must be sent from an email address of your domain name.
If you do not own a domain, many companies such as GoDaddy, Network Solutions, Google Domains, and others can help you to obtain a new domain with email.
To learn more about DMARC visit dmarc.org