Email Filters

Sending a marketing campaign by email is very easy, very cheap and a very effective method of communicating your message. However, because the sending of unsolicited email (spam) has been so rife in the past, some legitimate email campaigns can get lost in a spam filter.

So what is there to help? In this article we have twelve tips for you to help get your email campaigns to the intended recipient’s inbox.

  1. Double opt-in subscribers
    If your mailing list is derived from people signing up to your newsletter online then always use double opt-in. Double opt-in will send an email to the recipient asking that they confirm their email address. If you do not have an opt-in procedure at all then you could be sending unsolicited email and your recipients may report it as spam. If you use single opt-in where the email address is not verified then you could find that the email address is mistyped or someone entered another’s email address maliciously.
  2. Remove unsubscribes from contact lists
    You should make sure that when someone unsubscribes that they are removed from the mailing list. It is also preferable to only send to those that have subscribed to your mailing list rather than sending to a list that may have been established for another purpose. Some anti-spam companies’ setup honey pot email addresses that they post on the internet in the hope of capturing spammers.
  3. Spam word check campaigns
    There are certain phrases or words that have been traditionally used by spammers. Check your email against a list of spam keywords like free, shop, etc. Spam filters operate a spam keyword threshold and they assign each keyword a spam value. The spam filter will add up the values of spam keywords and if it exceeds the spam filters threshold it will block your email. So make sure you limit the number of spam keywords in your campaign. Check your wording for spam words. Try out the free simple spam word checker on My Web Minder.
  4. Keep true to subscription purpose
    Some spam filters link to a blacklist server that collects spammer details. Recipients can report your email as spam to these blacklist servers so to avoid them mistakenly doing so, make sure you only write to them on the subject(s) they opted in for. Do not send emails about car repairs to a recipient who signed up for a healthcare update. If you are emailing a regular newsletter, be consistent in your format by using a template, so that it is easy for the recipient to identify where it comes from rather than accidently reporting you as a spammer.
  5. Use more textual content than graphical
    Avoid sending emails with less textual content than graphical. When spam filters started checking the wording of a campaign, the spammers started putting their wording in graphics to avoid detection. Spam filters will likely treat your email as spam if more than 50% is graphical. You should avoid sending emails that are over 300Kb in size (inclusive of graphics and attachments) to a large audience.
  6. Oversized-text
    Do not use oversized text as spammers have used this method previously to attempt to capture a recipient’s attention. Likewise, excessive use of different colours, fonts and sizes should be avoided.
  7. No excessive styling
    Spam filters do not like excessive styling within the text itself as things like font and span tags have been used to break up spam keywords in the past so avoid tags within words (i.e. rather than “free” a spammer might type free). Try to cut down on style attributes within tags as too many repeated words may also get the spam filters attention (you can avoid this by style tags and apply style classes to the elements). Never make your text the same colour as the background as it looks as if you are hiding something and the spam filters will treat it suspiciously.
  8. Can-Spam rules

    Can-Spam is an anti-spam law passed in the United States, but in theory it applies internationally. The law defines what should be contained in an email to prevent spam.

    The law specifies the main aspects of an email that will help prevent it being marked as spam:

    • A valid subject and correct email header information
    • A legitimate sending “from” email address
    • An opt-out/unsubscribe option
    • Valid company and contact information in the email

    However, just because you comply with the above does not mean that your email campaign will get to its intended recipients.

    Remain Can-Spam friendly
    Every email you send should have an unsubscribe link and contact details as per the Can-Spam rules (see side bar). If you do not include an unsubscribe link some spam filters will look more closely at your email and may even just block it altogether. You should also make the unsubscribe process as easy as possible as you do not want someone reporting your email as spam because they couldn’t follow the process. Putting the company contact details on your email will help you conform to the laws of some countries. Also, if you have your contact details on the email it will allow a potential customer to get in touch.

  9. Remove bounces from contact lists
    If an email address has bounced several times you should remove this from the mailing list. Mail servers can usually differentiate whether the email is a hard bounce (i.e. email address does not exist) or a soft bounce (i.e. the recipients mailbox is full). It is a good idea to to keep your contact list clean by immediately removing any hard bounces and also to remove any soft bounces if they still bounce after a few attempts. If mail servers detect that you are constantly bombarding them with invalid email addresses they will suspect you are a spammer. If you are unsure about the validity of your contacts you can use the free email address checker at Valid Mailbox (there is also a paid for option if you want to have a whole list checked).
  10. Be open about who you are
    Never try to hide who the email is coming from. Make sure you have legitimate sender and return addresses as per the Can-Spam rules. Some spam filters will also look to see if the IP address of the server you are sending from matches the MX (mail exchange) records for the domain name of the sender. There is a registration service that will allow confirm the validity of a sender when sending from a different IP address to the registered MX records (do an internet search for “DomainKeys” or “DKIM”).
  11. Match parts in multi-part emails
    If you send a multi-part email then you should make sure your text part matches your html part word for word. Spam filters treat emails with different html and text parts as potential spam and assign it a higher spam keyword value. They won’t block it just because the parts are different but if you do run your campaign with different text and html wording, you will have very little leeway on spam keywords that are included.
  12. Always test your campaign
    You should always test your email campaign before sending to your mailing list. I have accounts with Google and Yahoo that I use as both operate different spam filtering systems. I also have other accounts that I send to when testing a campaign. I do not have a Hotmail account but it would be wise to try all of these to see if your email gets classed as spam.

Before you send to your readers it is always a good idea to send the email campaign to yourself to see if it gets picked up as junk and as mentioned above to try this with multiple accounts. Apart from your local mail client defences (such as Outlook or Thunderbird) or your internet security package detecting spam, you can also purchase software that acts the same way as a mail server would when filtering out spam (do an internet search for “no spam today for workstations” if you are interested).

Avoiding the spam filters for legitimate email campaigns

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