Email Marketing: How a SPAM Firewall Works (Q and A)

This whitepaper is in a Question and Answer format and covers ‘how a spam-filter works’.

Q: What actions can get me onto a blacklist or cause a spam filter to block our email?

Here are the main ways you can get onto a blacklist or have a spam filter block your otherwise good email campaigns: sbcglobal email login

    • Send an email campaign that receives too many SPAM complaints. When recipients get your email they can click the ‘This is SPAM’ button on their email client. This registers with spam filters as a ‘vote’ that your email is spam. Too many complaints and your emails will start going into the SPAM folder or will be outright blocked. Unfortunately some ISPs like encourage their users to click the SPAM button instead of unsubscribing, raising your spam rate. Many ISPs have a target complaint rate of less than 1 complaint per 1,000 emails sent.


    • Send an email campaign to one or more ‘SPAM Honeypots’. (See the next question for a definition of a SPAM honeypot).


    • Start sending a burst of emails from a newly configured email server at a new IP address. With spam filters, you are guilty until proven innocent. An IP address that has no email sending history that all of a sudden starts spewing out thousands of emails will look like a spammer firing up a new bank of email spam cannons.


    • Send an email campaign that has a high spam score (when analyzed by a spam content filter). If your email looks like spam content, some spam filters and blacklists will blacklist you for 48-72 hours.


    • Register your email server with an IP address that is ‘close’ to other IPs that have been flagged as SPAM email servers. Yes, it matters what neighborhood you ‘live’ in. Some blacklists will add your email server to their blacklist if your ‘neighbors’ are known spammers. The logic is that either you may be associated with the spammer, or you are hosting your email at an ISP who is willing to host spammers, so you are guilty by association.


    • Send emails to a list with a lot of hard bounces (invalid addresses). SPAM filters track the % of invalid emails you try to deliver. If your hard bounce rate is consistently high (greater than 15% for example), your email reputation will fall and you may be blacklisted for windows of 48 ~ 72 hours.


    • Configure your email servers incorrectly. True spammers can be lazy and often do not configure their email severs correctly. Well, at least that is the opinion of most spam filters and blacklists, so if your equipment is not configured correctly, your emails may be blocked.


  • Send email campaigns to general email lists and aliases such as support@, sales@, webmaster@, info@ and so on. These are often aliased to dozens or even hundreds of recipients and it is highly unlikely that a person will register on a website using such an address, so you are likely to irritate many recipients and generate spam complaints.

Q: What is a “SPAM Honeypot”?

There are blacklists that work directly with registrars to ‘re-cycle’ domains when they expire. Send an email to an address at one of these domains and you will get stuck in their ‘honeypot’. Some honeypot-based blacklists are more devious. They actually host websites with embedded email addresses. Utilities that crawl websites and parse out email addresses (which is illegal in the US anyway), will capture the honeypot addresses.

Blacklists that are based on honeypots use this logic. When a company goes out of business or a domain otherwise becomes invalid, you should not be sending emails to anyone at that domain anymore. If a company is out of business for say, 6 months, and you send an email there, then either a) you are not using good list management practices, and should be ‘penalized’ to clean up your act or b) you likely purchased or automatically generated the email address by combing websites for email addresses.

Q: Do “Spam Honeypots” actively subscribe with bogus data to e-mail lists?

No; however malicious hackers and bots sometimes crawl sites and may register email addresses on signup forms that are from a dead domain that could coincidentally, have been ‘harvested’ by a honeypot blacklist. This is one of the reasons to use double-opt-in forms on your website to validate that the email addresses used are valid.

Q: Can I get a list of SPAM Honeypots so I can avoid them?

We all wish! No. This would defeat the purpose – if blacklists made their honeypot addresses visible or available, any spammer would just use these addresses as suppression list and avoid the honeypots. These addresses are always changing as blacklist managers/vendors are constantly registering new domains.

Q: What are the best practices in reducing my email marketing campaign bounce rates?

Ideally, remove contacts that have not received an email in more than 9-12 months – see the explanation for ‘SPAM honeypots’ above. Use valid contacts who have opted to receive your emails. Also if you have received a ‘soft bounce’ error for an email address after 4-5 attempts, it is best to remove that address from your list. Most ESPs (Email Service Providers) do this automatically.

Send to your clients / email contacts more frequently – at least once a month if possible (assuming you have newsworthy information to send). Most Email Providers automatically remove the invalid email addresses that accumulate each month as people change jobs and move.

Q: Do email bounce rates impact our email marketing reputation and deliverability?

Yes. Some SPAM filters track information on your % of delivery to invalid addresses (hard bounce rates) over time. If hard bounce rates are consistently high, (15% or more for example), then your email reputation will fall and you will be blacklisted.

Q: To check our email sending reputation, which IP address should I use when checking?

Check the IP address of the email servers that are sending your email. If you are using an ESP, ask the ESP for the IP addresses that your account is using or sharing. If you are sending emails from your own in-house servers, ask your IT team for the IP address of your outbound email servers.

Note that there are also blacklists that are based on your ‘top level domain’. This is the domain that is used to send your emails. If you are using an ESP you can ask what the sending ‘top level domain’ is, or you can forward an email to yourself and check the email header (or ask IT to help you determine this).

Q: Could we improve our damaged email reputation by changing our IP addresses every 6 months?

This would almost always harm your reputation, unless you are a spammer. Spam filters and blacklists accumulate historical email delivery information for the IP address of your sending email server(s). Over time, if you are sending relevant, high quality permissions based email, your reputation will *improve* over time. On the other hand, if your practices include purchasing large cheap lists, or not maintaining your lists by removing unsubscribers and hard bounces, your reputation will go from bad to worse. In this case, you might improve your email reputation by moving to a new IP address but if your company is not employing good practices, you will simply burn though new IP addresses every 6 months, which may upset your ISP enough to consider terminating your service.

Q: If I have recipients in my list that never open my email, do these non-responders affect my sending reputation?

At present, probably not. However if you have contacts in your email list that have not opened a single email of yours in 6-12 months, why do you want to keep sending to them? You might be better off sending a final re-engagement campaign to these unresponsive contacts (see earlier question) and deleting contacts who do not respond.

Q: I have email recipients that block my email campaigns. I have done everything. Why is this?

Assuming you have verified that your email spam score is low and that your email servers are not on any blacklists, it is still very common to experience some email being blocked by spam filters. Some IT organizations set their spam firewalls to very conservative settings, often unknowingly creating more problems for end users, since a higher percentage of valid email may be blocked. In this case your options are:

Contact the end customer directly and request that they add your email address to their address book. Local inbox settings usually over-ride general settings and this should permit your email to get through

If the recipient is getting your email but it consistently ends up in the spam folder, have the recipient click ‘this is not spam, and request they add you to their address book (above).

Contact the recipient and provide the IP addresses of your outbound email server (if you are using an Email Service Provider (“ESP”), ask the ESP what IPs you are assigned. Provide these IPs to your recipient and ask them to request that their IT department add the IPs to the corporate whitelist / non-blocklist.

Otherwise, consider removing these contacts from your list. Note that, if a recipient’s email filter responds that your email is being blocked after multiple campaigns, most Email Services Providers will automatically remove the contact from your list or flag the address as undeliverable after some number of failed ‘soft bounce’ attempts.

Q: How many links can I use in my email marketing campaign?

Based on analysis of our B2B customer data, adding more links will almost always improve response rates. Key points to consider:

  • Try to include a link within your initial opening paragraph (Read More.. for example). This can increase overall click rates by 12-15% and is virtually always the top-clicked link of a campaign.
  • Do you know where the second best performing link is? In the ‘P.S. or Footer section! Don’t be afraid to ‘advertise’ or promote below your signature.
  • Work more links into your campaigns. Our analysis shows that campaigns with more links produced higher total click response rates while not increasing the unsubscribe rate. 15-20 links in a campaign is not unreasonable.

Please check my other postings for more email marketing tips.