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16 Tips to Improve Email Delivery

Many recipients get so much mail that they only read e-mail that:
Criteria #1: Seems to have a legitimate subject and source, and...
Criteria #2: Is convenient (meaning they didn't have to do any extra work to get your message).

It's the marketer's constant battle to meet both of these, and most of the battle is involved in criteria #2 and getting past those sometimes-overzealous spam filters. With so many different types of spam filters, you can improve your chances of reaching your target audience using a variety of different techniques. Here are some tips and tricks I've learned over the years to help navigate legitimate marketing messages past the filters and into the inboxes.

The first step of the battle is always to understand what spam is. Quite simply, spam is any e-mail that is sent to a large group of people without having prior permission. (

The content of your e-mail doesn't matter, so even if you're not selling Rolex replicas or weight-loss supplements, your message is still spam if you're sending it to a group of people without their prior consent.

Tip #1: Don't Cut Corners
Spammers cut corners. Limit the number of recipients to 1 per e-mail instead of trying to cut corners and cramming a bunch of recipients into each message.

Tip #2: Use the Right Tools
If you're using PHP, then use phpMailer (, which is a free PHP application. phpMailer gives you a lot more control over the different options when you're creating mails, and gives better structure to the e-mail than the built-in PHP mail() function. For example, you can add friendly names like Bob Johnson to your To/From addresses, and later add HTML content or attachments if you want. You should also change the X-Mailer header within phpMailer to be something like boltMail (just a random name). This should help avoid any sort of spam filters that check for mails that originate from a web programming language like PHP or ASP.

Tip #3: Avoid CC and BCC
Send 1 message per 1 recipient, and if someone NEEDS to be copied for quality control purposes or something, then use BCC during your test runs, and turn it off when you're ready to send the real mailing. Never use CC in mailings. Not only does it go against Tip #1, but it also violates the privacy of anyone being CC-ed, since everyone can see everyone else's addresses. (Plus, if spammers see one of the messages, they could harvest the other addresses for their spam lists.)

Always try to preserve the privacy of each person on your mailing list.

Tip #4: Avoid Spammy Words and Phrases
Seems simple enough, but you'd be surprised at how often small businesses will throw words like "guaranteed" into their proud statements about their service. Most spam messages make over-the-top claims in order to survive being deleted immediately, so things like guarantees and free offers and words in all-uppercase tend to make legitimate messages look like spam.

Check your e-mail content to make sure you're not using these types of words or phrases. Side note: I've never used this service, but I've heard lots of good things about InboxInspector, which is supposed to check your e-mails to see how well they fare against different firewalls and spam filters, and how they'll look in different clients. (I don't know if it costs anything) 

Tip #5: Set up Reverse DNS
DNS is becoming more and more important. Specifically reverse DNS (or pointer / PTR records) is a type of record set up by your hosting company or by THEIR internet provider that lets them update the IP address of your mail server so that when some 3rd party asks to see what domain name an IP address belongs to, they'll be told that it's your domain name / mail server. Setting up rDNS isn't something that is done overnight usually, so put in the request and explain to your hosting company what you're trying to do. They should be able to help you, and if they can't, then they're probably not a very good hosting company, and you can find a hundred better ones. I personally use JaguarPC ( and have been with them for about 5 years now (but ask the ISP about rDNS before signing up).

Tip #6: Use DomainKeys and/or SPF
DomainKeys and SPF (Sender Policy Framework, not sunblock)? What are those? Here's a quick explanation:

I could write a snail mail letter to you, but put down Bob's address as the sender on the envelope, and drop it in just about any mailbox in the U.S. and it would probably still reach you. However, YOU have no way of knowing whether it's REALLY from Bob or someone pretending to be Bob (in this case, me). If the postmark said it was sent from a post office in Arizona and YOU knew that Bob ONLY used the post office next to his house in California, then YOU would know that it probably was not really from him.

This same idea, but with e-mail, is where SPF and DomainKeys come in. They are basically lists of mail servers that YOU have declared "okay." It's as if you said, "Okay, these mail servers can send mail using e-mail addresses with my domain name in them."

Then, when the recipient receives an e-mail, the recipient's mail server looks at the domain of the From e-mail address. Then, it looks up the list of mail servers that are approved to send mail for that  domain. Once it has that list of approved mail servers, it then looks at what mail server actually DID send that message. If that mail server isn't in the approved list, then the recipient server can say, "This message is probably coming from a spammer who just faked their From address."

Whoever controls your DNS (possibly your hosting provider) should have access to set up these tools. If you have a network administrator that does these things, then have him/her go to for some help with SPF and for help with DomainKeys.

Tip #7: Monitor the Blacklists
Blacklists are quick ways to stop your e-mail from being delivered. Blacklists are simply services (usually free) that have lists of mail servers that send out spam or for whatever reason, should not be trusted to send good mail.

Try this free tool here to check your mail server's IP address on all the major different blacklists: 

Unfortunately, blacklists are tricky beasts that all work differently. Some have actually died but the service is still available and simply never updated with real content. Normally, no self-respecting mail administrator would make use of a dead blacklist, but you should still make sure you're not on any of the others.

This tool should also give you links that take you to that particular blacklist's web page so you can see details about if, (sometimes) how, (sometimes) why, and (sometimes) when you were blocked. Most blacklists will give you a way to de-list yourself, and it usually takes them at least 24 hours to process your request. Just make sure you're not having to de-list yourself multiple times at the same blacklist - that would indicate something evil afoot.

Tip #8: Close the Relays!
The way to get yourself (nearly) instantly blacklisted is to have an open relay. An open relay is simply a term that refers to a mail server that has no proper security set up, and basically allows ANYONE to send e-mail to anyone else for free.

If you, or someone on your IP address (sometimes even close to your IP address) has an open relay, then you need to figure out a way to shut it down. Open relays are used by spammers a LOT because they can send their junk mail through without any worries in the world and it doesn't affect them or cost them a thing. Spammer heaven. If you're unlucky enough to be in the same range of IP addresses as an open relay or someone else that has been marked as a spammer, then you need to contact your hosting company and have them deal with that other person.

Also, NEVER EVER try to send your mail through a known open relay. That's the quickest way to get your entire e-mail address domain banned.

Tip #9: Make Use of Captcha
If you have any mail forms on your site, then you may want to try adding captcha onto them. Mail forms, while not exactly open relays, can almost be used as ones if they let the visitor specify the To address anywhere where it could be changed (even in a hidden field). Sometimes all it takes is one spam message to somebody who then reports it to the blacklists. Fortunately, the blacklists are there to help, not to harm, so most will give you second chances and help you with advice on how to prevent yourself from getting listed again. Usually they don't mention open forms like this, because they're not too common, so this is a just-in-case-you-have-one-of-these comment.

Tip #10: Use Proper HTML
Be careful when sending HTML mail (if you do this in the future) - if you send badly-formed HTML, it can count against you in some spam filters. Badly-formed HTML can be anything from invalid HTML tags to tags that were not closed properly or have invalid attributes. Try running your HTML through a validator like the one at W3C before sending it:

Also avoid creating HTML messages that contain a high image-to-text-content ratio, since that's also a red flag for a lot of spam filters (remember all those spams with almost no content but one big image that had stock quotes in it?).

Tip #11: Don't Send Mail from a Cable/DSL/Fiber Connection
Most consumer-grade Internet connections get dynamic IP addresses. A lot of spam is sent from home PCs that are infected with hidden worms that blast out mail over the home connection, while most legitimate, business email comes from fixed, dedicated IP addresses. If you send mail from a dynamic IP address, many spam filters will instantly reject the message, no questions asked.

Tip #12: Don't Use Excuses
Spammers often use the phrase "You are receiving this because you signed up for..." because they're trying to appear as if they have a legitimate reason to sell you the latest weight-loss drug. Legitimate e-mails don't really use this phrase because the recipient usually knows exactly why they're receiving it (because they signed up for it). Another red flag for spam filters.

Tip #13: Always Let Them Unsubscribe
ALWAYS include a link for unsubscribing and ONLY send to people who have requested your newsletter or whatever it is. Some marketers don't want to include this because they're afraid of losing subscribers.  Besides being a legal requirement, allowing recipients to unsubscribe also means that you're not wasting your bandwidth on people who will probably just delete your message without reading it.

On a side note, you should never unsubscribe from mailings that you never subscribed to. Sometimes this is just a spammer trick to get you to click on something in the email that will alert the spammer that someone is actually reading mail at your e-mail address.

Tip #14: Spend Money on Whitelisting
As a worst case scenario, there are whitelisting services, which are basically the opposite of blacklists. Whitelists tell servers that your e-mail is good. Whitelists are often expensive, too.

There is a service called Habeas which is a popular whitelist and they have a lot of cool toys for tracking your e-mails. The downside is the high cost. For just about every project I've ever come across, they are prohibitively expensive. So you'll have to weigh the potential ROI of your e-mails against their cost. If you're not selling anything, or if you're not a really big company, then chances are it's not going to be worth it to spend $5k to $20k just to whitelist your newsletter. (The 5k to 20k is just a rounded range of quotes that I've received from them - you would need to check with them for more accurate pricing).

Someone mentioned to me that Hotmail has one, but that would probably be limited to Hotmail users (I might be wrong on that).

Tip #15: Avoid Bad Attachments
Try to avoid sending any attachments, but if you do, make sure you're not sending .EXE files, password-protected ZIP/RAR/other-compressed files, .BAT, .COM, .PIF, .ELF, or any other sort of executable program file.

If you DO need to send a program attachment of some sort, then put it into an unprotected ZIP file so it can be scanned by the recipient's antivirus scanner. Even .DOC files are becoming hard to send without putting them into ZIP files. Generally, ZIP files and images are almost always safe to send. I've seen filters and scanners choke at least once on just about everything else, from MS Word docs to Powerpoints to proprietary formats to OpenOffice files. PDFs are iffy - it's a popular format to send, but many filters and scanners now have the ability to understand PDF files, and if the PDF files are written by a program that doesn't do it right, then that could cause problems, too (so stick it in a ZIP file to help).

Tip #16: Never Buy Mailing Lists
It can be very tempting to marketers to purchase 3rd party mailing lists. Those lists are often touted as having great returns and having only valid addresses, but those two claims are usually lies. Not only does using a 3rd party mailing list mean that your message is spam (because the people on the list haven't opted in to receive YOUR emails), but worse, the real outcome is that all of your emails (current mailings and future ones) will often get blocked. Here's how:

These lists are usually created by spammers harvesting e-mail addresses off of message boards and web sites without any sort of rhyme or reason. If it looks like an e-mail address, it goes into the list. This means that these lists will often contain lots of e-mail addresses that are old, or don't even go to a specific person (e.g. So these are just bad addresses to begin with.

However, the real kicker is that more and more companies are also putting fake, "lure" e-mail addresses  (called honeypots) onto their web sites and hiding them in the web page source code. Normal people don't see these honeypot addresses, but spammer programs harvest them right up with all the other addresses and add them all to their mailing lists. At this point, the spammer's mailing list has been poisoned with this special honeypot e-mail address.

Then, when you buy the list and send an email to the honeypot address, the spam filters will be able to tell that you are using a mailing list purchased from a spammer (there's no other way you would be sending to that honeypot address), and they'll instantly block all mail coming from you. So, it's NEVER EVER a smart thing to purchase a mailing list, no matter what the mailing list vendor tells you. They'll lie through their teeth to get your money and they don't really care about your returns, so steer clear.

In summary, if you're not sure whether your own email counts as spam, then spam filters almost certainly will count it as spam. In the long run, it costs more in time and effort and money to send out something that will get blocked by 99% of spam filters than to just not send it at all. So if you're really sending legitimate mail, then using these tips should give you a decent head start on getting your e-mails through to your recipients.

Copyright © 2009 - Jonathan Hilgeman. All Rights Reserved. 

Comments (10)

Most Valuable Expert 2023
Distinguished Expert 2023


Oops - I think I posted this comment as a private comment. Let me repost.

Hi Jason,

If you have experienced employees in your marketing department, then there's no real major advantage or disadvantage that I've personally seen. The services often just do the same job, and it all comes down to rates, salaries, and other needs of your company.

Paid marketing services come in all shapes and sizes. Some do more than others, but ultimately, they still need your cooperation to fully manage the mailing list (because opt-outs can also come from people calling in, sending separate e-mail requests, web site opt-outs, or even snail mail ... although I've only ever seen an opt-out request via snail mail once in my life). Managing opt-outs can be the most time-consuming service, so if they can get into some sort of "groove" and be able to manage it without your help, then that could be a major load off of the shoulders of your marketing employees.

That said, I've used different marketing services, but never Topica, and I've never dealt with C.C. as a customer of theirs, so other people may have a better, more valid opinion than I do on this topic. You should follow jhoekman's suggestion and post a question to get other people's input. I don't really participate in that zone, but it'd be interesting to hear the results.
Most Valuable Expert 2011
Author of the Year 2014

Good article.  As a veteran of many years of broadcast email I can add a couple of comments.

1. There are legal penalties for getting it wrong.  Some of these involve handcuffs.  Do not send spam, full stop.

2. I've used Constant Contact with slightly better than excellent success.  We looked at a handful of broadcast email services; the church staff liked the CC interface best.  Prices and services were comparable across the board.  It would be an understatement to say they have been worth many times what we pay for their services.

3. There is no end to the electronic vandalism in this area.  Earlier this year (2009) a worm picked up a honeypot address and sent unsubscribe notices to every mailing list it could find.  The mailing lists politely replied with messages to the effect of "you are not subscribed to this list."  The result?  Thousands of false-positives for spam, causing mail lists to get blacklisted all over the world.

The spam situation is only going to get fixed when the governments impose severe penalties on the services who send and forward the spam, not just the spammers.  Once that happens, the SPF and other electronic anti-spam measures will become popular solutions and capable legal defenses.  As of now, we are still mostly unable to trace the email back to its source and confirm that the source originated the message.  Until that happens, Constant Contact and its ilk have an iron-clad business model.
Most Valuable Expert 2023
Distinguished Expert 2023


I agree with Ray and add a story about the importance of getting the best bang for your buck, even when the bang doesn't come cheap.

Recently I had a former boss contact me about ways that he could do mass mailings for cheap - he had looked at CC and thought they were just too expensive. He had tens of thousands of addresses (which is a lot to a relatively new company), so he kept shopping around and kept finding cheaper and cheaper and even cheaper email service providers  (ESPs). I gave him a warning - all ESPs are out to make money, so if they're cheap, then there's a good reason behind it, and it's not just goodwill.

It costs money to purchase and host servers, and that cost is built into ESP pricing. When an ESP's pricing is too good to be true, then you're probably sharing one server with dozens of other companies who want to send out as much email as possible for as little as possible. These other companies are usually spammers trying to sell you all the things you delete from your inbox or that get caught in your spam filter.

As soon as these other companies start mailing, the server they use almost always gets blacklisted. This means that even though YOU aren't sending spam (hopefully), you're sending it from a blacklisted server / address, and the majority of your invested money into this email campaign will simply go down the toilet, because almost all of your recipients will never even get the chance to read your email in order to decide whether they want to take further action (buy your product or whatever).

Getting back to the story, he finally chose an ESP and asked if I heard of them. Some quick research on the web about that ESP validated everything that I had said, including a few more horror stories about the ESP just taking the money and never responding to complaints or support requests.

Usually we make good decisions about quality versus cost everyday. If you need a a good screwdriver or some pliers, you don't buy it at the 99-cent store, because usually that tool will break after 1 or 2 uses, which ends up just being a waste of 99 cents. Even if you bought two more screwdrivers at 99 cents each, you'd have spent almost $3 total to get 3-6 uses out of it and you wouldn't have a working screwdriver at the end. Instead, you usually spend $3 at a place like Home Depot or something and buy a slightly more expensive screwdriver that will last you for years.

Email is the same - don't try to go cheap just to save money, because you'll be losing your marketing dollars. There are other good email providers besides CC, but remember that "You get what you pay for" is extremely applicable within the email realm.
Alan HendersonRetired marine engineer

Excellent advice.

Evan CutlerVolunteer Chief Information Officer

Absolutely an awesome article,
it got me moving forward.

Very Succinct and easy to understand.
Thanks much.

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