Occasionally, you or your users might send mail that bounces because the recipient blocked your IP address. When an IP address is blocked, all mail from the address bounces. Some domains use a denylist service to identify and block mail from suspected spammers. If enough users mark mail received from a particular IP address as spam, the service can block that address. Even if one of your messages goes out from an IP address that was blocked after someone else used it to send spam, your mail can bounce.
Option 1: Get added to approved senders
Ask the recipient to add your domain name to their approved senders list.
Option 2: Have recipient allow IP addresses
If the recipient’s mail service doesn't support approved senders, the recipient's IT admin should add Gmail's sending IP addresses to an allowlist.
Note: You can find the current range of Google IP addresses by checking Google's SPF record.
What Google does to help
Google regularly asks denylist services to remove our IP addresses if they get blocked. However, because we can't prevent services from blocking any of our IP addresses or guarantee the removal of them, Google doesn't remove IP addresses on a denylist.
Contact Google Workspace support
If you have additional questions or concerns, contact Google Workspace support.