Bounces are responses received from the receipt SMTP server and categorized as INTERNAL, SOFT and HARD. There are multiple reasons for bounces such as “user unknown”, “over quota”, “network rejection” etc.
Spam complaint is triggered by receipt end, the mailbox providers such as Yahoo, Gmail, Hotmail provide the option such as a button to their user to report any spam to their spam protection system. There can be many reasons when a user clicks on the spam button such as didn’t opt-in for your email, they find some suspicious content, you keep bothering and don’t honor their unsubscribe request. Every mailbox provider has own algorithm to treat spam reports, more spam complaints can lead to serious damage your sending domain and our email server IP address.