Blocklists and spam traps are two of the main reasons email gets blocked. This article explains how they work, how to avoid them, and what to do if your email is blocked.
- Blocklists
- Spam traps
- How to avoid blocklists and spam traps
- If your email is blocked or rejected
- Set up abuse contacts for your domain
Blocklists
A blocklist is a list of IP addresses or domains that are known to send spam. Mail servers and spam filters check incoming email against blocklists and may reject email from a listed sender. Legitimate senders can end up on a blocklist too, for example after a few complaints or spam trap hits.
Anyone can run a blocklist, so they differ a lot in quality and influence. Large mailbox providers mostly use well-known lists such as Spamhaus, SpamCop and URIBL. To check whether an IP address or domain is listed, use a checker such as MXToolbox.
Senders with large volumes have their own IP addresses in Symplify. Smaller senders share pools of IP addresses with senders who have similar sending habits. If you don't know which IP addresses you send from, contact support@symplify.com. Symplify monitors the major blocklists and contacts you if your sendouts cause a listing.
Spam traps
A spam trap is an email address that exists only to catch senders with poor list practices. Hitting spam traps lowers your reputation and can get you blocklisted. There are two types:
- Pristine traps were never used by a real person. They are hidden on websites and collected by programs that scrape addresses. Hitting one means addresses on your list weren't collected with permission.
- Recycled traps are abandoned addresses that a provider has turned into traps, after first returning "unknown user" bounces for a long time. Hitting one means you keep sending to addresses that stopped working.
Spam trap addresses are secret, so you can't simply find and remove them. Prevention is the only reliable approach.
How to avoid blocklists and spam traps
- Only send to contacts who signed up. Bought, rented or scraped lists, and old addresses taken from a CRM, are the most common cause of blocklisting. Use double opt-in where you can. See Custom Optin.
- Remove inactive contacts. Addresses that never open or click can turn into recycled traps. Use the Engagement filter and see Healthy lists and permission.
- Protect your sign-up forms. Use a CAPTCHA, reject malformed addresses and role addresses such as abuse@ and postmaster@, and ask for the address twice if typos are common.
- Make unsubscribing easy and say at the top of the email why the contact receives it.
- Use a sender domain your contacts recognize from when they signed up.
- Keep a steady frequency. Sending too often, or so rarely that contacts forget you, both increase complaints.
- Handle replies and complaints quickly. Some contacts try to unsubscribe by replying.
If you have hit a spam trap, find the source before you send again. Look at which list or segment was sent in the period of the hit, and check that no bounced or unsubscribed addresses were included. Split the suspect segment into smaller parts and send to them one at a time to narrow it down. Send a re-confirmation email to the suspect addresses and remove those who don't respond.
If your email is blocked or rejected
Blocks often show up as policy-related bounces in your bounce statistics. Some blocks caused by blocklists or reputation are not shown as bounces in Symplify. If contacts at one provider stop receiving your email, contact support even if you see no bounces. See All about Bounces.
Before you ask to be unblocked, find and fix the cause. If you don't, you will soon be blocked again, and providers are less willing to help repeat cases.
- Find the cause. Compare the time the problem started with your recent sendouts. Look for higher than usual bounces, complaints or unsubscribes, and for new or old lists that were included.
- Check your setup. Make sure your sender domain is authenticated with SPF, DKIM and DMARC, that you use your own tracking domain, and that your abuse contacts work (see below).
- Read the provider's sender guidelines. Most large providers explain their requirements and how to request a review:
- Contact the provider or blocklist. Have your business details, abuse contact, sending IP addresses and domains, sign-up URL, unsubscribe method and privacy policy ready. Explain what went wrong and what you have changed, without being defensive. "This wasn't spam" doesn't work; "An old list was included by mistake, we have removed it and changed our process" does. Expect an automated reply first and a slow response.
Symplify receives complaint reports from the mailbox providers that offer feedback loops and counts them in your statistics, so you don't need to register for those yourself.
If Symplify has told you that your sendouts caused a blocklisting, fix the cause first, then contact abuse@symplify.com for help with delisting. If your sendouts put the shared sending infrastructure at risk, Symplify may move your account to other IP addresses or pause sending until the problem is solved.
Set up abuse contacts for your domain
Providers, blocklist operators and recipients contact senders through standard addresses. Create abuse@ and postmaster@ on every domain you send from, and make sure someone reads them.
Also register your domains with abuse.net. Many mail administrators use it to find where to send complaints about a domain, so registering means complaints reach you and you can act on them. The abuse.net website explains how to submit your domain and contact addresses.