Fix email bounces due to blocked IP address

Fix email bounces due to blocked IP address

See the full article from Google Kb.
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 sender's 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.