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Improving Email Deliverability

The following guidelines contain everything we know about improving email deliverability and getting your message heard.  Junk mail filters these days can be very sensitive, and it is important to know what they are looking for.

This article is primarily intended for users of Gammadyne Mailer, but most of these guidelines apply to email in general.  As always, Gammadyne reminds you not to send spam.

Content Guidelines

  • Explain to the recipient why they are receiving the email.
  • Include an opt-out link.
  • Don't use a free email address, like hotmail or gmail, in the From: header or in an email hyperlink.
  • Don't link to an IP address.
  • Personalize each email if possible.  Identical mass emails are more likely to be flagged.
  • List plenty of contact information, including your physical address.
  • Obey the CAN-SPAM Act.
  • Include a List-Unsubscribe header.  Recipients will be more likely to unsubscribe instead of filing a spam complaint.  The header should look like this:

    List-Unsubscribe: <mailto:unsubscribe@example.com>

  • Don't put your content in one large image.  Many email clients do not display images by default, and many spam filters don't like this.
  • The content of the email could cause it to be flagged as spam.  If it contains phrases like "buy viagra" or "penis enlargement", this is a dead give-away.  Unfortunately, the spam filter probably does not report which phrases it is flagging.  Experimentation may be required.
  • Don't use a subject that is Title Case or ALL CAPS.
  • There should be an empty <title></title> element inside the <head> element, despite the fact that the title is meaningless in an email.
  • The HTML code should be validated for correctness.  In Gammadyne Mailer, click the Validate CSS and Validate HTML buttons below the Raw HTML code.  Also, run the "Troubleshoot HTML" tool on the Test menu.
  • The Sender must be a valid email address that will readily accept email.
    • What we refer to as "the Sender" is the email address that is reported to the SMTP server with the MAIL FROM command.  Normally this is the same as the From: header.  In Gammadyne Mailer, the Sender can be specified separately from the From: header (on the Headers branch).
    • Bounce-backs are returned to the Sender.
    • Be sure to prevent this mail account from filling up.  For a large mailing, you may have to receive emails from it even as the mailing is still underway.
    • The Sender is logged within the email as a Return-Path: header.

Delivery Guidelines

  • The email must be relayed from a computer that has a static IP address (web servers have these, residences do not).  Also, there should be a "Reverse DNS" record for the IP address.
  • Many domains don't like it when a lot of mail arrives from one source quickly.  For mass mailings, it would be prudent to limit the delivery rate.  In Gammadyne Mailer, go to the Send/Throttles branch and enable the Universal Domain Throttle feature.  A rate of 1 email every 12 seconds is recommended as a minimum.  If time is not important, you can throttle it back even further to achieve a higher success rate.
  • The computer sending the email and the relaying SMTP server should have the clock set to the correct time.
  • When using Gammadyne Mailer's Direct Delivery mode:
    • Launch the "Check PTR Record" tool (on the Tools menu).  This will tell you if Direct Delivery is possible.
    • Go to the Send/Delivery branch and check the "Override EHLO Domain" box.  Then click the "Detect Domain" button.

Reputation Guidelines

  • Keep the mailing list clean of bad addresses.  After performing a mailing, remove all hard bounces from the mailing list.  Excessive failed delivery attempts can result in blacklisting.  For this task, it is important to use software like Gammadyne Mailer that can distinguish between a hard bounce (e.g. permanent failure) and a soft bounce (e.g. mailbox full).

    Furthermore, this is doubly important because some ISP's will reactivate old email addresses and use them as spam traps.  Once you send email to a spam trap, future emails will be blocked.
  • Use double opt-in.  This ensures that no one gets signed up without their permission, and greatly reduces the chance that you will be reported for spamming.
  • Use the "Check Blacklisting" tool to determine if your IP address is blacklisted.  You should also test the IP address of the relaying mail server, and any sites that your email links to.  Once blacklisted, it is necessary to request removal from the organization that runs the blacklist.
  • Do not purchase mailing lists.  Such lists are likely to be full of bad addresses, and will generate a high rate of complaints that can result in blacklisting.
  • Do not harvest addresses from web pages.  You are likely to harvest a spam trap address.  Once you send email to a spam trap, future emails will be blocked.
  • Use Sender Policy Framework (SPF) to prevent spammers from impersonating your mail server.
  • Check the reputation of the IP address for your computer and mail server with the following sites:
    AOL
    http://www.cyren.com/ip-reputation-check.html
    http://www.sendmail.com/sm/resources/tools/ip_reputation
    https://www.senderscore.org
    http://www.trustedsource.org
    Time Warner Cable

Note:  We no longer recommend using DKIM.  It is not a relevant nor useful standard.  In fact, RFC 5863 states that '...messages with invalid signatures need to be treated no better and no worse than those with no signature at all'.

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