Deliverability - how to manage your Email reputation

Managing your reputation is a bit like SEO, there are some well-defined technical rules which are mostly easy to follow and which make up the the biggest part of your reputation. And then there are some softer and a bit more fuzzy rules which are harder to detect and follow.

Technical rules

Have a clean DNS setup

• Your mail server’s forward and reverse DNS name must be identical.

  • It should be a real host name, not a generic and dynamic name given to you by your provider, like ip-123-123-123-123.myprovider.com.

• It may use the same top level domain name as your Email sender address but this is not mandatory.

• Your domain name must have an existing and working MX record. Though it does not have to be the same server as the one you use to send your Emails.

• The mail server specified in the MX record must have a working “postmaster” address.

Strictly follow RFC rules

• i.e. handle the SMTP protocol properly, obey return codes and timings

  • Most common SMTP server software does this correctly, so if you are using a “regular” mail server without tampering with its core rules too much you should be fine.

Handle bounces correctly

If you keep sending Emails to an address which no longer exists your recipient’s mail server will notice and downgrade your reputation.

So make sure to no longer send Emails to addresses with bounces. In the Universal Messenger you can define a maximum number of bounces until the address will automatically be removed from all lists.

Keep your Mail server IP and your domain name out of SPAM blacklists

There are multiple so called Real-time Blackhole Lists (RBL) on the internet which maintain lists of DNS domains or IP addresses suspected to send SPAM Emails. Those lists are read and written by most Email providers and if you are listed your Email reputation will be badly affected. Most providers might not accept Emails from you any more.

From time to time it might happen that despite your best efforts your server’s IP address or your domain name is listed on RBLs. If you follow the rules it will be unlikely but not impossible. Sometimes a range of IP addresses is listed, that can happen for example if you are just renting a root server and other root servers from the same subnet are actually sending SPAM mails.
It is therefore important to regularly check the lists. The good news is: getting removed is usually as easy as writing an Email to the list provider and wait an hour or so.

To track your listing you can use The Spamhouse Project (https://www.spamhaus.org) or MX Toolbox (https://mxtoolbox.com/).

Configure your Message-ID to contain your sender domain

Certain email providers expect the Message-Id header to end with the official sender domain name. Set cmsbs.mail.messageId.hostname accordingly.

Format of Message-ID header as sent by UM: UM.<delivery_ticket>@<domain>

delivery_ticket is the Delivery Ticket of the outgoing email.

By default, domain is the name or the IP address of the SMTP server given in cmsbs.mail.smtpserver. This part can be overwritten via cmsbs.mail.messageId.hostname.

Optional technical measures

There are a number of technical measures which help improve your reputation but are not strictly necessary.

Create an SPF record

Sender Policy Framework is a method to confirm the authenticity of your domain name used in your Email’s FROM header. The IP addresses of all your mail servers which are used to send Emails for your domain name must be registered as legitimate in your DNS. Many Email providers will honor this and only accept Emails from your domain by the mail servers registered. The downside is that you may only use those servers for all of your Emails, so if you are planning to use the same domain name as your regular Emails it can have an impact on your overall mail server setup. But the existence of an SPF record in your DNS will in fact improve your reputation.

Use DomainKeys (DKIM)

You can use DomainKeys to confirm the authenticity of both your mail servers and the legitimacy of the Email content. Like SPF it uses DNS to identify your mail servers but also registers cryptographic keys which are used to sign your emails. If your mail server is capable of signing all outgoing Emails this might be the most reliable solution, but you can also use the Universal Messenger built-in DKIM capability.

Honor delivery limits

Many Email providers have limits of how many Emails from a single IP address will be accepted within a certain time frame. Unfortunately those limits are not fixed and most providers will not disclose their limits and they may even vary depending on your reputation. So it is important to regularly check your mail server log for error messages indicating a limit has been reached.

Most of the time hitting the limit will mean that your Emails will still eventually be delivered but with a time penalty of up to a few hours.

You can define limits for outgoing Emails per recipient domain name in the Universal Messenger (described here: Optimizing send performance ).

Use different (sub-)domains for your newsletters

If you use a dedicated (sub-)domain for Emails sent from the Universal Messenger or even for every type of newsletter it is easier to manage the settings mentioned here without affecting your regular company domain. It is highly recommended because it helps keeping your Email setup clean.

Warm up your IP address(es)

Every new mail server will need to be “warmed up” in order to build a reputation. Installing a new mail server and send thousands of Emails from that server on the same day will not work. Many mail providers will most probably not accept those Emails because that is basically how SPAM networks work.

You have to slowly start sending Emails from that server. There are lists on the Internet describing best practices to warm up your IP addresses, e.g. https://sendgrid.com/docs/assets/IPWarmupSchedule.pdf.

It might seem counter-intuitive but the more Emails you send over a longer period of time the better your reputation will become.

Make it easy to unsubscribe

At first glance, this might seem like a bad idea, but it is actually important that recipients can easily unsubscribe. If users just mark your Emails as SPAM to get rid of them instead of having an easy way to unsubscribe it will hurt your reputation.

• Include a visible link to unsubscribe in your Email footer; in some countries, especially in the EU, this is even mandatory by law.

• Add a List-Unsubscribe header to your Email.

  • Here is a good explanation of how and why: https://www.litmus.com/blog/the-ultimate-guide-to-list-unsubscribe/

  • Here is how you can add headers in Universal Messenger: https://www.universal-messenger.de/knowledge-base/intern/doc-en/Developer/Mail_options.html

Use whitelisting

The Certified Senders Alliance (CSA) is an Email whitelisting service which is recognized by many Email providers. If you are a member you can register your mail servers after fulfilling an extensive list of technical requirements and organizational guidelines.

Non-technical rules

Those rules are less well defined and can only be regarded as general guidelines or hints. Plus, like with SEO, they can keep changing.

Use double opt-in

Depending on your country this might even be a law, at least within the European Union it is. Before sending a newsletter to a recipient make sure to have their explicitly accepting receiving Emails from you. The most common method is double opt-in, i.e. after an Email address has registered they will receive an Email which asks them to accept the registration.

If you use the UM Newsletter App it will use double opt-in as default.

Make your Email content less suspicious

Many Email providers use heuristics to determine whether an Email is suspicious of being SPAM. The content or overall look and feel of an Email may be evaluated in the process. There are some general rules which help improving the probability of looking clean:

• Less images, more text

  • Email which only consist of one large image may be especially suspicious, so try to balance images and text.

• Personalize correctly

  • Using the correct recipient name e.g. in the salutation at the beginning of your Email may help.

  • Use full name in TO header

• Avoid URL shorteners

  • Some providers like Gmail find it suspicious if you mask your links with URL shorteners like bit.ly.

• Avoid suspicious keywords, especially in your subject

  • It may be obvious but it is better not to use common keywords used in SPAM Emails like names of male enhancement pharmaceuticals.

• Do not excessively use caps

  • An acronym from time to time is ok, but do not yell at your users, especially in the subject

There are services which check your deliverability like https://www.emailonacid.com/email-previews/.