How to handle delays and greylisting patterns?
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Your email gets to the server. You wait for the delivery confirmation. Nothing. Then 15 minutes later, it arrives. Or sometimes it takes an hour. What's happening is greylisting. It's a legitimate anti-spam technique, and it's not a problem you need to panic about. But you do need to understand it.
Here's how greylisting works. A server receives your email and says, "I don't recognize you. Try again later." This is a temporary rejection, not a bounce. Your email server (or your ESP) automatically retries. Real senders retry. Spambots don't. So servers accept the mail on the second attempt. The legitimate mail gets through. The spam disappears. It's elegant and it's why you see 10 to 30 minute delays on first sends to a new domain or IP.
Is this normal? Yes. Once a server has seen you a few times, it stops greylisting your mail. Your subsequent sends arrive faster because you're now recognized. If you're warming up a new IP or sending from a new domain for the first time, expect delays on early sends. This is fine. Let it happen. It's part of building trust.
When should you worry? Watch for changes in greylisting patterns. If you've been sending from an IP for six months with no delays, and suddenly every send gets greylisted for 45 minutes, something changed. Your IP reputation might have dropped. You might be on a new blocklist. Your domain might have authentication issues. Increasing delays are a warning sign, not a feature.
How to respond to concerning delays. First, verify that your SPF, DKIM, and DMARC records are passing. Use MxToolbox to check. Check your IP on Spamhaus and other major blocklists. If you're on a list, that explains the delays. Request removal. If you're not on any list and authentication passes, the delays are likely just normal greylisting. This is genuinely not a problem. Your mail will arrive.
Your next step: check when your greylisting started. If it's new, verify your authentication. If it's been steady and predictable, you can ignore it. Most ESPs handle retries automatically. You don't need to do anything.
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