We've noticed a trend where some customers see sudden ISP Blocks and soft bounces from Google only for specific email messages, hinting at issues with the content and links. Gmail's bounce notifications suggest that the issue might be related to suspicious content or links within the message. Upon closer inspection, we found that all the blocked messages included free URL shorteners, particularly bit.ly links, which are commonly used by spammers to hide malicious websites and files. To avoid similar issues, we recommend using original URLs whenever possible, especially when tracking links in your emails, and consider using reputable link tracking services like Postmark's high-reputation domain to optimize deliverability. Additionally, valid HTML, CTAs, and plain text copies can also impact email deliverability. There are best practices guides available for transactional and broadcast sending that can help improve deliverability.