Gmail can generate false positive SMTP bounce responses for various reasons, including temporary issues like greylisting, network problems, or a recipient's account being recently deleted. Inaccurate bounce codes, problems with DKIM/DMARC/SPF records, a poor sender IP reputation, spam filtering, sending too quickly, and poor list hygiene (spam traps) also contribute. Distinguishing between temporary (4xx) and permanent (5xx) SMTP errors is crucial. Monitoring sender reputation, verifying recipient addresses, and ensuring proper sending infrastructure configuration are important considerations.