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Email marketing, as many of us know, can be a powerful, inexpensive method of reaching our most active potential or existing customers. It can boost not only our direct sales, but also our credibility and referrals.

One of the major benefits of email marketing is that email is free, but obviously this is the same reason why spam has become so popular and so frustrating. With spam comes spam filters and with spam filters comes the blocking of legitimate email.

In this article I’ll try and describe the basic steps that can help reduce the number of emails you send out that get blocked by spam filters — hopefully resulting in a more rewarding marketing effort.


The right selection of words

Many spam filters work by analyzing the email based on its content and the words used. Many words — such as free, sex and so forth — are very heavy spam trigger keywords. Your priority should be to avoid such words while keeping your newsletter as professional as possible.

Later in this article I will show you a technique that I use to help me detect words that could trigger spam filters that I may have missed.

Email content and design

  • Don’t include too many images in your email (1-2 per email should suffice) or some filters will flag it
  • Don’t use images or send attachments that are too large. 300Kb should be the absolute max size of the email so be sure to make sure the total for images and attachments comes in well under that (adding a file to an email will increase the size by about 30% just in encoding it) so you need to take that into consideration too
  • Don’t include a single large image in your email if you can avoid it since this is how most spam nowadays seems to operate.

Email Best Practices, Things you can do to improve your email delivery:

  • In a broad sense:make sure that whether you are adding subscribers or they are adding themselves, it is quite clear to them that they're giving you permission to receive email messages.
  • More specifically:Don't use purchased leads
  • Ask people if they want your email and don't simply assume that they do based on another transaction with you or your business
  • Use Confirmed Opt-In to protect your sender reputation
  • Promptly Remove Unsubscribes Responsible email senders automatically remove subscribers who opt-out using the link at the bottom of any of the messages sent from your campaign.
  • Use a reply address you check regularly
  • Manually remove people who ask to be unsubscribed
  • Send frequently enough ... But Don't Overwhelm Sending too frequently can cause an increase in: Complaints & Unsubscribes

Review Your Message Content: Once you're finished at the drawing board and have saved your message, review it and make sure:

  • It has a plain text version, even if you've written one in HTML
  • You've avoided using excessive punctuation within words and phrases
  • There is a sufficiently high text to HTML ratio -- messages should not consist of large images with little text
  • Also, by sending a test of your message to a few of your own email accounts, you can help ensure that it appears consistently the same way to each of your subscribers.
  • Get Whitelisted: Encouraging your subscribers to add your email to their address books has benefits.
  • Along with the subject of your message, the first thing your subscribers see of your messages when they're browsing their inboxes will be the reply address and/or the "Name" you also set.
  • You reply address and name should be Recognizable and Hosted at the same or similar domain as the website subscribers signed up at and avoid using free addresses (e.g. hosted at yahoo.com, gmail.com, hotmail.com, etc.) you use for personal communications.
  • Don’t use a free email address as your “from” email Instead of using your free/personal email address such as @hotmail.com or @gmail.com you should use an email address for the company or organization for which you are sending email.
  • Don’t use your email address for the "from" and "To" email address: If you send a email that is “from” your email (let’s say test@activecampaign.com) and you send it to a subscriber with the email (test@activecampaign.com) it will most certainly be marked as spam as the “from” and the “to” is the same.
  • Send using a consistent “from” email address: We do not suggest changing your “from” details often.  Keeping it consistent can help build your reputation.
  • Don’t send a single graphic/image: Sending an email that only contains a graphic is a sure-fire way to have delivery issues.  You should take the time to design an email with text and graphics.  Not just a single image.
  • Test different subjects & email contents Content does play a major role in filtering email.
  • Avoid using all caps, spammy sounding content, etc.. By testing different subjects and email contents you can test responses & delivery.
  • Pay attention to your links in your email Spam filters check the URLS that you are linking to. If you link to a domain that has a poor reputation you will be penalized
  • Don’t include links that use link shortening service.
  • Your links should be full links to the real URL.  You could experience delivery issues using shortened links from link shortening services.
  • Take the time to code your HTML correctly Improper HTML tags, broken tags, etc.. could reduce your email delivery.
  • Remove inactive subscribers Delete your old & inactive subscribers.
  •  Never include Javascript, form code, or video within your email This is an absolute way to get filtered: We suggest to link to your video or include a screen shot of the video.  You can include a screen shot of the full video component which will look like the video is embedded.  When your user clicks the play (or any part of the video image) it would then open the video in their browser.
  • Avoid copying anything directly from Microsoft Word, Excel, Powerpoint, etc..: When you paste content directly from these applications additional characters (that you do not want) will be automatically added.
  • Don’t test using the same phrase as your subject and email contents.   If you send an email with a very similar subject and message body it will likely be filtered as spam.  (example would be having the subject set to “this is a test” with the body set to “this is a test”).

Pay attention to your formatting

When formatting your email, keep it simple and professional. Excessive use of different colors, fonts, sizes, images and so forth will result in a higher spam filtering rate. Keep your email as clean as possible, and try to stick to a maximum of 2 or 3 different font types and sizes. Overly large sized fonts will surely add to an email being flagged as spam, as will too many images (or not enough text).

Try and use a short and simple stylesheet rather than using font tags excessively. Most spam filters don’t appreciate a multitude of font tags and inline formatting, and the more primitive filters can’t detect stylesheets so they will not penalize as easily.

Consistency is king

Use a template if you plan on sending newsletters consistently. This will make sure that all your newsletters look and feel the same. It will also add a touch of professionalism and branding to your newsletters.

Whilst not directly affecting spam filters, this will enable your readers to distinguish your newsletter instantly, thus not reporting it as spam accidentally. Some spam filters work by querying a spam server, whereas others report individual emails as spam. If your email gets reported as spam, then more than likely multiple spam filters will flag your email.

Being consistent with your timing of the newsletter also helps. For example, if you send a newsletter once per month (I personally don’t recommend you send out any more than this, unless you’ve got something really interesting to say), then aim to send it out at the same time, on the same day each month.

Once again, your potential readers will learn to expect your email, adding professionalism and often improving open rates, also reducing accidental spam flagging as well.

Keep your lists as clean as possible

Honor all unsubscribe requests (your email marketing software should generate an unsubscribe link for all emails you send) and process bounced emails frequently. Sending to email addresses that have bounced repeatedly can result in a blacklisted IP address. You want to make sure that each bulk email you send does go out to legitimate, working email addresses.

You should also make sure your abuse@ and postmaster@ emails are valid and working. The Internet Engineering Task Force (IETF) has recommended these email addresses for complaint spam reporting and you may receive emails from users or ISP’s if they have a complaint or spam report about your mailings.

Unsubscribe and Contact Information

Every newsletter you send out should contain a way for the reader to unsubscribe. Not doing so is illegal in some countries and is an instant sign of spamming. You should also display your contact information (Phone, Fax and Address) clearly, as this greatly increases confidence in your email and your company, as well as conforms to spam laws in the United States. Contact information also allows a potential customer to contact you if need be.

Test, Test, Test

The key to avoiding spam filters is testing. The first method of testing I use is to send the newsletter to multiple email accounts with existing spam filters. For example, I have a Gmail (http://www.gmail.com) account and a Hotmail (http://www.hotmail.com) account that I make sure I send my newsletter to. If the newsletter ends up in the junk folder, then I’ve got some work to do.

I also have a couple of email accounts with different web hosts that have spam filters in place. In particular, they mostly use spam assassin — a popular piece of spam filtering software. Spam assassin is useful because every email that it flags as spam is given a report and a list of why that email was considered spam.

I also use a powerful spam filtering tool, which detects any spam related "triggers" based on Spam Assassin’s scoring system. The scoring system is constantly updated so you will always stay on top of the latest spam filter changes. By using the spam assassin checking system — gives me feedback as to why my email may have been flagged. If I’ve used words or formatting that I shouldn’t have, or if I’ve included too many images, etc.

More Ways to Avoid the Spam Filters

  • Watch your attachments
    Many people don’t realize that the type of attachment you send with your email can cause different spam filters to block your email and even go so far as reporting your I.P to a black list database.

    You should avoid using script or any type of attachment besides PDF. Many corporate mailboxes as well as virus filters block attachments that end in .exe, .avi, .swf, .zip, etc.

  • Use double opt-in lists
    I’ve mentioned this in my previous article but once again to make your mailing list as clean as possible always use double opt-in strategies. That is, when someone signs up they should receive an email which contains a link they must click to verify that they do indeed want to be on your mailing list. This stops illegitimate email addresses from being added to your mailing list.

Why would you care about your SMTP send email limit?

When you are about to send several emails at a time (for a business or personal event, as a newsletter or else), you MUST know your SMTP mail server restrictions, so your email account does not get temporarily or permanently blocked by your own email or Internet provider.

Then, you can use an email marketing software, like Maillist King (Business Edition 199.5USD, Personal Edition 99.5USD) to schedule your outgoing emails in order to match the send email limits of your provider.

Why ISPs or web hosting providers have email-send limits?

Email spamming can be very annoying to email users, but it is also expensive to Internet providers. Spam emails are consumming mail server resources and bandwidth - as a result, one solution for most Internet, email or web hosting providers is to fight spam by preventing their own customers for sending spam-like emails.

A simple method to prevent customers from sending bulk emails is by enforcing limits to send emails (for example, you are not allowed to send more than 500 emails per day). However, this popular method has its downside, as it prevents trustworthy customers from sending many legitimate emails at a time (not spam).


Although there’s no fail-safe way to absolutely guarantee all of the emails you send will reach the intended recipients, simply by applying the techniques described in this article can dramatically help to improve your email deliverability and hopefully your click thru rate and bottom line.

In conclusion, I hope that you’ve found the above tips useful and I wish you luck with your email marketing endeavors!