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Have your e-mails already been flagged as spam, although you’ve sent a seemingly legitimate proposal to your client? Have you ever wondered why the efficiency of your newsletter campaigns suddenly dropped down? In both cases you deal with a problem which is harder to get done with than you think it is: bulletproof e-mail delivery.

The main problem with undelivered mails is that both sides — sender and recipient — don’t really know what happened. Was the e-mail sent? Is the task done? Was the e-mail delivered? Most recipients will never know that an e-mail flagged as spam was sent to them — they just don’t receive the e-mail. And most senders will never know that an e-mail flagged as spam wasn’t delivered — they just don’t get a response.

This article suggests over 20 bulletproof techniques, best practices and related services you can use to ensure best e-mail and newsletter delivery rates.

[Offtopic: by the way, do you know the Smashing Network has its own Smashing Network RSS Feed? Only excerpts are displayed in the feed.]

Where Do We Stand?

E-mail is a primarily mean of communication in the Web. Instant messaging supplements e-mail, however it’s a choice when it comes to communication with people you know well and/or you have a regular contact with. So where do we stand? And what is the main problem with e-mail delivery? And why do we have to deal with it?

1. Spam-filters calculate “spam score” to detect junk mail.
   To determine whether a given e-mail is spam or not most spam filters consider a number of different attributes, such as content, length, percentage of text, use of images, number of recipients, headers etc. Usually they calculate the so-called “spam score” for every e-mail which passes the server.

   If the mail’s score exceeds a certain threshold the mail is blocked and lands in the spam folder. The level where the threshold is set is defined by the mail server configuration. By default, this spam filter flags messages with a score greater than 5 as spam.

2. Spam filters aren’t perfect.
   Over the last years the efficiency of spam filters used by e-mail software clients and web-based e-mail-services has improved dramatically. However, since the strength level of anti-spam-algorithms has increased, it’s inevitable that also more legitimate e-mails don’t get through them. The result is that these filters, in order to block a good percentage of spam mails, block a good percentage of “suspicious” — in reality non-spam — messages as well.
3. Newsletters remain important, RSS-feeds haven’t made the breakthrough yet.
   In its recent usability study Nielsen Norman Group found out that news feeds are definitely not for everybody, and they’re not a replacement for email newsletters. Apparently, “feeds are a cold medium in comparison with email newsletters. Feeds don’t form the same relationship between company and customers that a good newsletter can build.

   [..] Given that newsletters are a warmer and much more powerful medium, it is probably best for most companies to encourage newsletter subscriptions and promote them over feeds on their website.” Therefore it’s important to be aware of some sound techniques to pass through anti-spam-filters and thus guarantee a good newsletter delivery.

4. E-mail delivery is tricky.
   The fact is that in most cases you never really know whether your first e-mail adressed to someone who doesn’t know you and/or isn’t expecting your e-mail will come through mail filters. And since the recipient doesn’t expect your mail he/she won’t be able to take it into consideration. Therefore it’s necessary to be aware of some techniques to ensure the delivery of your e-mails.

Best Practices For E-Mail Delivery

According to latest studies, your reputation determines your email delivery more than your content. So if you meet the expectations of your readers / recipients and don’t send irrelevant information you improve the delivery rates of your e-mails. Apparently, “most delivery challenges are due to subscriber feedback; such feedback typically takes the form of complaints by recipients who mark the message as “spam” in their respective email clients and problematic traffic patterns such as bounces and spam trap hits.”

However, it’s not always enough. Let’s take a look at the best practices for optimal e-mail delivery rates.

1. Avoid follow-ups, ask for a brief feedback — one word “soon” is enough.
   Since you don’t know whether your e-mail is delivered or not, don’t assume that it is delivered. However, don’t send a follow-up in doubt; follow-ups which usually include the copy of an original e-mail aren’t effective and get on recipients’ nerves. Instead ask the recipient in the first message to send you a brief note that your e-mail was received. For instance, ask to write back “soon”, “got it” etc. once they’ve received the e-mail — indicate that no further comment or instant reply to your mail is necessary.
2. Don’t attach large files to your first e-mail (unless specified by the employer).
   Instead provide the detailed information on where the your CV and portfolio can be found on your personal web-site. Or simply copy and paste your resume in your e-mail. Compressed files (.zip, .tar etc.) and images are still strong signals for spam detection algorithms.
3. Use a consistent senders’ name and email.
   Make it easier for your recipient to recognize you. Don’t change from “Max Mutermann” to “Developer’s team”. Don’t change your e-mail suddenly. Once your recipient has mistakenly considered and reported your message as spam you are likely to never be able to contact them again.
4. Never put a link before important information.
   Once the recipient has clicked upon the link you’ve provided and landed on some page he/she has no information about, you’re lost. Many recipients might not get back to your message and report you as spam.
5. Snail mail is bulletproof.
   If possible, follow-up on your e-mail with a “snail mail” version sent to the real postal address. This is a great way to establish contact and stay in touch with a person! Reference the e-mailed version you sent (including the date, time, and subject if possible). [Source]
6. Avoid fictional or irrelevant sender’s name.
   Communicate with your recipient personally. Instead of nicknames or company titles use your first and last name. Notice that spam-filters award e-mails without sender’s name (or with an empty name) with spam score points. The sender’s name shouldn’t include numbers or symbols rather than your actual name. Instead of “no-reply@yourdomain” or “admin@yourdomain” provide your readers with concrete and short contact information, e.g. “Max Mustermann” . The “reply-to” field shouldn’t be empty.

Best Principles For Bulletproof Newsletter Delivery

Since newsletters are still an important part of marketing campaigns, to achieve the highest response rate you’d like to ensure the highest delivery rate. The principles and rules listed below might help you to increase the delivery rate of your newsletters.

1. Send newsletters regularly.
   Let your subscribers know when your emails are coming. If you offer a subscription to your newsletter from your web site then tell each and every subscriber exactly when to expect your newsletter. [Source]
2. Tuesday / Wednesday 2-3pm = Increased Response.
   Your subscribers will come to “expect” your email to arrive in their inbox on the same day at the same time every week, meaning that they want to read your content and are generally more receptive to any special offers or promotions you may include. This means that they are less likely to misunderstand your newsletter and report it as spam. [Source]
3. Slow down your newsletter delivery.
   Instead of using tools which boost your newsletter through mail servers to achieve “instant delivery” prefer “slow” delivery tools. Avoid sending mails to multiple (dozens or even hundreds) recipients using CC:-attribute. Use professional newsletter software or professional e-mail-delivery services. “When ISPs detect a flood of email, it looks like the work of a virus or a spammer.” [Source]
4. Use a tag line at the beginning of the subject line.
   Mark your newsletters as such. Make it easier for your readers to recognize your newsletter. E.g. ‘[SM Newsletter] Nr. 297, 16.10.2007 — Usability Glossary — Splash Pages — Big Typography’. Remain consistent. Otherwise your readers might consider your e-mails as spam and report it. [Source]
5. Always insert the current date in the content.
   A correct date which indicates when the newsletter was sent is more important than you probably think it is. If the date isn’t mentioned or is provided incorrectly, the newsletter is given spam score points.
6. HTML is OK, but only if MIME-Multipart is used.
   When sending newsletters as HTML make sure that also the plain text version is attached. Messages sent in MIME-Multipart-Format are automatically sent in a way that subscribers without active HTML-Viewer still get a decently formatted e-mail. It is important that both plain text and the HTML-version have the same or very similar content. The percentage of text should be higher than the percentage of HTML or images. Keep your message size between 20 and 40 Kb.
7. Use CSS sparingly.
   In most cases it is better to use inline CSS-styling in HTML instead of referring to CSS-file in HTML. However, referring to external CSS-files is better than sending them with newsletter.
8. Avoid graphics and complex HTML-elements.
   Spam-filters consider a number issues related to HTML. For instance, if the newsletter has too many closed tags, too many graphic (images) or structural (tables) elements it gets just as many spam score points. Besides, many readers use software (e.g. Outlook) which automatically blocks images; if users don’t understand what the mail is about they’ll report is as spam. Complex HTML (particularly if more than 50% of HTML-code are HTML-tags) is generously awarded with many spam score points — keep it simple. Colorful backgrounds, tables, JavaScripts and web forms shouldn’t be in newsletters.
9. Motivate your users to add you to their whitelists.
   To ensure the bulletproof e-mail-delivery ask your readers to add you to whitelists. You can create Email whitelist instructions in seconds — for a number of e-mail applications.
10. Screen your advertisers and partners.
    If your newsletter includes a link to a blacklisted web site you might get a whole bunch of spam score points. Verify the sites and e-mails you are linking to; check if they are already blacklisted or were reported as spam (or spam sources) before placing their advertisements in your newsletter. Even if the company is legitimate, it is possible that spammers have used their accounts for sending out spam mails.
11. Monitor new subscribers.
    Monitor new subscribers in your lists. Set suspicious “spamflag” addresses such as “abuse@”, “nospam@”, “postmaster@”, “marketerspam@” as inactive subscribers. [Source]
12. Verify your subscribers with signup confirmation.
    Always make your mailing lists double opt-in. This means that when a user subscribes to your mailing list, they will be sent an email with a link that they must click on to confirm their subscription. This is very important because many people can accidentally enter an incorrect email address, or even the email address of someone else on purpose. When that person receives a newsletter they did not subscribe to, they will assume they have been spammed, and your newsletter (and possibly your web server) will be reported as spam. [Source]

    It also keeps invalid email addresses off of your list, which reduces the volume and percentage of undeliverable messages that you send. Since undeliverable rates also factor into filtering rules, keeping invalid email addresses from being subscribed to your list will help you to avoid content filtering. [Source]

13. Test your newsletters before sending them out.
    Always check the “spam score” of your newsletters with Free Content Checker, SpamCheck, Contactology and further tools (most of them are listed below).

Tools and Services

Before sending the newsletter out you are likely to check whether your content will get through most spam-filters. Since spammers always come out with new ideas of tricking filters and filters are being updated all the time even absolutely innocent mails can land in the junk folder. Let’s take a look at some tools you can use to check your e-mails once they’re ready to be sent.

Spamcheck offers you the possibility to check your content via e-mail or through the Spamcheck online form.

Once you’ve provided the sender’s information, subject and the content of your e-mail, Spamcheck evaluates it rewarding the e-mail with spam score points and provides you with a SpamCheck Report. As most filters, many different aspects are taken into consideration; if your e-mail has 13 points or more you can be sure that it won’t find its way to your recipient’s inbox.

SpamAssassin Tests is the list of indicators currently implemented in SpamAssassin, the #1 Open-Source Spam Filter used on most Apache servers. This list describes the indicators and the spam score an e-mail gets if this aspect is found in the e-mail. A score higher than 5 points typically indicates that a message strongly resembles spam, and would possibly be blocked or filtered by major email providers or ISPs. You might need to time to understand what the indicators are and what you should do to minimize your spam credit. However, it’s worth it.

Sparklist Content Checker runs a free test of your e-mail through Spamassassin and presents you a detailed “spam check”-report with possible “false signals”.

Contactology offers a spamcheck per web form. The Message Quality Score (MQS) used by Contactology allows you to quickly determine a message’s quality and deliverability on a scale from 0 (bad) to 100 (excellent). You can check the likelihood that the message will be blocked by spam filters given the content of the message and all the message headers and the likelihood that the message will look as intended in all mail readers.

In our test one of our e-mails had the score of 92. Not bad, but it can be improved.

Among commercial solutions you might want to check out Delivery Monitor. Delivery Monitor is a powerful tool for gaining valuable, real-time information about your campaigns—are they being delivered at all and, if so, are they making it to recipients’ inboxes. Use Delivery Monitor to determine if your mail is automatically routed to “spam” or “bulk” folders at more than 50 different ISP’s and email providers, then take corrective steps to delivery more mail to the one place it will be read — the inbox. The tool provides real-time feedback about email deliverability, highlights delivery issues and indicates if deliverability problems arise during a campaign, so you can pause the mailing until the issues are resolved.

Mailchimp Inbox Inspector is an optional add-on to MailChimp account that allows you to check your email marketing campaigns instantly. It generates the screenshots of a sample promotional email, rendered in 16 different email programs, points out problems with spam filters and corporate email firewalls as well as broken links and typos.

Campaign Monitor is built for designers who can create great looking emails for themselves and their clients, but need software to send each campaign, track the results and manage their subscribers. You can see screenshots of exactly how your email will look in more than 15 of the most popular email clients like Outlook 2007, Windows Live Hotmail, Yahoo, Gmail, Lotus Notes etc. Instead of scanning your content for “spammy words”, the tool passes emails through real spam filters and tells you exactly why you failed. The e-mail is also run through a number of key spam firewalls – the gatekeepers for most ISP’s and large corporations.

The tool also provides a comprehensive set of real-time reports allowing you to accurately measure the effectiveness of every campaign you send.

References, Sources

• HTML Email Guide
• CampaignMonitor
• Email tips
• Keywebdata
• Octeth
• Wired
• iMedia
• Newsletter Archive
• Anatomy of Spam Filters
• HTML Email Mistakes
• Avoid Spam Filters