What are the most common ESP-related deliverability issues?

Your deliverability just tanked. Before you blame your audience or your email copy, check if your ESP setup is actually the culprit. It happens more than you'd think.

Authentication is the biggest gotcha. SPF records need to include your ESP's servers, or inboxes will be suspicious. DKIM has to be set up right. Your keys and your domain need to match, or the whole thing falls apart. DMARC alignment is where most people get lost. You've got to make sure SPF and DKIM are both pointing to the right place. If you're using a custom sending domain, all three have to be talking to each other. This is fixable if you catch it early.

Shared IP reputation can tank you through no fault of your own. You're sharing an IP pool with thousands of other senders. If someone else on that pool is spamming, your inbox placement suffers too. The ESP's supposed to manage pool quality, but not all of them do it well. Some customers just get stuck in a bad pool. Your only escape is to move to a dedicated IP or switch ESPs (neither fun). If you're consistently getting poor placement despite clean list practices, ask your ESP about pool quality.

IP warmup failures happen when senders go too fast. You've got a shiny new IP and you want to send right now. But if you dump a million emails into a brand new IP on day one, mailboxes will reject them. You've got to ramp up gradually. Most ESPs have specific warmup guidance. Ignore it at your peril. Interrupted warmup (where you pause and restart) is almost as bad as skipping it entirely.

Bounce handling is simple in theory, brutal in practice. Your ESP should automatically suppress bounced addresses so you don't keep sending to dead email addresses (that kills your reputation). If they're not suppressing bounces properly, or if they're misclassifying them, you'll keep hitting bad addresses. Check your bounce report and make sure suppression is actually working.

Tracking domain problems are sneaky. Your open and click tracking routes through a domain. If that domain gets blocklisted, your emails get flagged. Some ESPs use shared tracking domains (meaning you share it with other customers). Custom tracking domains are safer but require more setup. SSL certificate issues on tracking domains can also trigger spam filters.

Platform-specific issues happen. Some ESPs have slower queues during peak sending periods. Others have hard limits on how fast you can send. Technical glitches on their end happen too. If you're seeing unexplained delivery drop-offs and it's not auth, reputation, or warmup, ask your support team directly what's happening.

Want to start troubleshooting? Pull your last campaign's delivery report. Check which issue above might apply. Then hit your ESP's documentation or support team with the specific question. Most of these are fixable once you know what's wrong.