The 'rate limit exceeded' error in email delivery indicates that you have surpassed a sending threshold imposed by the receiving mail server or your ESP. This is commonly triggered by reputation-based throttling, sudden increases in sending volume, or practices that resemble spam. Troubleshooting involves reviewing bounce logs, analyzing sending patterns, improving sending reputation by warming up IPs/domains, implementing proper authentication (SPF, DKIM, DMARC), cleaning email lists, implementing feedback loops, staggering sends, and adhering to the specific sending guidelines of each email platform. Addressing API rate limits may require implementing exponential backoff strategies or reducing maximum connection settings.