A spam complaint is when a recipient of an email marks the email as spam. This typically occurs when the recipient feels that the email is unsolicited or unwanted, and they want to prevent similar emails from being delivered to their inbox in the future.
When an email is marked as spam, it is usually reported to the sender's email service provider, which may take action to prevent similar emails from being delivered in the future. This can include adding the sender's domain or IP address to a blacklist, which can make it more difficult for the sender's emails to be delivered to other recipients.
It's important to avoid sending spam emails, as they can damage your reputation and make it harder for your emails to be delivered in the future. To avoid spam complaints, it's a good idea to follow best practices for email marketing, such as obtaining explicit permission from recipients before sending them emails and providing an easy way for them to opt out of future emails.