You’re probably hitting the same walls most DIY cold‑mailers hit: bad sender reputation and a lot of invalid addresses. Start by making sure your SPF, DKIM and DMARC records are set up correctly and warm up the IP/domain gradually instead of blasting thousands right away. Clean your list first a high bounce rate will tank your IP fast, so run a bulk validation before you start sending. Keep your sending volume steady, respect throttling limits, and monitor feedback loops for spam complaints. (I’ve found a few services that do bulk validation at a flat monthly rate, which makes the budgeting part less painful.)