The visible parts of an email (subject line, body content, etc.) carry your message to the customer and also play an important role in deliverability. However, there are also other factors that are not visible to you or the customer but which can have a major negative impact on deliverability.
In this article we offer some guidelines on how to avoid these pitfalls when building your email campaigns.
Email File Size
Making your email content too large not only slows down the generation and launch of the campaign in Emarsys, it can also affect the deliverability and impact of your message. The Emarsys content editor monitors the size of your email campaign as you build it and will warn you if it goes over our recommended threshold in the Deliverability Advisor.
How big is too big?
It is hard to set a firm limit for email size, firstly because this is very hard to measure in any editor, and secondly because deliverability is strongly influenced by reputation. However, we would suggest that 102KB is a threshold above which deliverability rates will begin to decline.
Why is smaller better?
In most cases, emails are the means to an end: you want the recipient to click through to a landing page where they can complete a form or make a purchase. Keep your message simple – too much information in the email will distract them from this purpose.
Furthermore, some web and mobile clients such as Yahoo or Gmail also collapse emails larger than 102KB and hide the content behind a Show full message button. This puts an extra, unnecessary step between the recipient and your goal.
What affects email size?
The easiest way to judge the size of your email is simply to look at the preview: longer emails with many images are larger than shorter, text-only ones. Attachments, which should always be avoided in marketing emails, will also pile on the bytes.
Aside from these, there are many hidden elements that will affect the size of an email.
- Images are the most obvious culprits. Reduce the size of inline or background images and remove unnecessary ones. Most importantly, host your images externally.
- Responsive design is an essential part of today’s email marketing but this also carries hidden weight, so factor this into your estimation.
- Text versions are critical to ensure good deliverability and although small in size, it all adds up.
- Overly complex HTML can increase the size of an email with no added benefit. Make sure that you remove any redundant code.
- Hidden formatting tags from content editors. If you write your content in, for example, MS Word, and copy & paste it into your editor, it can happen that hidden tags are copied across. Not only will these increase the email size, but they can also cause the text to render badly in some mail clients. If you use such an external editor, we recommend to clean up the content by pasting it first into a plain text editor such as Notepad.
- Line breaks and spaces are also useful to pay attention to. Eliminating the unnecessary ones reduces the message size.
You can read how to optimize your email in our Guidelines for HTML Email. If in doubt, you can also contact Emarsys Support and ask our Web Production department to review and optimize your code for you.
With a multipart/MIME message, both an HTML and a text version of the email are sent at the same time. It is important to send multipart messages with both content types because:
- Spam filters expect marketing messages to be multipart with two versions.
- Some (albeit few) email clients do not recognize HTML, or may not support elements of your HTML code.
- You guarantee that even those recipients with ‘non-smart’ mobile phones and PDA’s can surely read your email.
- Some people simply prefer plain text emails.
In Emarsys, a text version is automatically generated and sent for template-based email campaigns. The content is based on the HTML content, and cannot be edited. For custom HTML campaigns, the default text version is empty but can be created independently.
Multipart messages can still be spam
A multipart email can still fall foul of spam filters if:
- It does not contain all the required headers and MIME parts (see below).
- The message has only the text or HTML MIME parts instead of both.
- The message has only text and no images.
- The text version is very different from the HTML version.
- Too many images and not enough readable text is sent, so the overall HTML has a low text-to-image ratio. The ideal ratio of text to image area for the HTML is 60/40. Making full use of the Text version of the email is a good way of boosting this ratio.
The make-up of a multipart message
Below is a more technical breakdown of what constitutes a multipart message.
The multipart/alternative content type is used when the same information is presented in different body parts in different forms.
Through the use of the multipart/alternative content type, email messages have parts arranged in a tree structure. Please note that no other content types are recommended for marketing messages (e.g. the multipart/mixed or multipart/form-data content types must not be used).
Parts and their content types
The multipart/alternative with the same content in text/plain and text/html content types results in a message sent in both plain text and HTML. Please note that the content type for text with attachments is not mentioned as no attachments are recommended in mass mailings; images must be hosted externally. Plain text messages, replies, embedded media, or forms are also not suggested.
Example of an acceptable marketing email
X-sender: <email@example.com> X-receiver: <firstname.lastname@example.org> From: "Senders Name" <email@example.com> To: "Recipient Name" <firstname.lastname@example.org> Message-ID: <email@example.com> Date: Mon, 14 Dec 2015 13:24:02 -0400 Subject: Sample Multipart Message MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_DC7E1BB5_1105_4DB3_BAE3_2A6208EB099D" ------=_NextPart_DC7E1BB5_1105_4DB3_BAE3_2A6208EB099D Content-type: text/plain; charset=iso-8859-1 Content-Transfer-Encoding: quoted-printable _**Sample Text Content**_ ------=_NextPart_DC7E1BB5_1105_4DB3_BAE3_2A6208EB099D Content-type: text/html; charset=iso-8859-1 Content-Transfer-Encoding: quoted-printable <html> <head> </head> <body> <div style=3D"FONT-SIZE: 10pt; FONT-FAMILY: Arial">_**Sample HTML Content**_</div> </body> </html> ------=_NextPart_DC7E1BB5_1105_4DB3_BAE3_2A6208EB099D--
- the plain text portion follows the Content-Type text/plain header,
- the HTML portion follows the Content-Type text/html header.
Why are text versions important?
The most important role that a text version plays in a multi-part email relates to deliverability. However, they are also a good back-up for devices which can only render text, and you should always consider that some people may simply prefer to receive your messages in this format.
Text versions improve deliverability for the simple fact that spammers rarely invest the time to create one. Therefore most spam filters focus on this and the text-to-HTML ratio of an email when assigning it a spam score.
To calculate the text-to-HTML ratio, the spam filters decode the entire message and count the characters in plain text versus those inside HTML tags. Since images, formatting and links take up a lot of HTML code, having a text version is a great way of boosting your plain text count and getting above the threshold below which a spam filter will treat your mails as suspicious.
You can take 30:70 as a benchmark threshold ratio for text to HTML.
What makes a good text version?
When creating your text version, keep it short and simple. Take the most important information from your email and present it in a clear visual way.
Also remember that you will not have visual aids such as colour or font size so pay attention to the visual effect of the text version and make use of white space. Make it easy for the reader to scan the message and don’t use dense blocks of text that will put them off.
Here are some useful tips to keep in mind when creating your text version:
- Structure the content clearly so that reader knows at once what you are trying to tell them.
- Clearly identify your call to action, for example by using angle brackets as arrows: >>> Product now available! <<<.
- Use simple characters such as *** and +++ to break up paragraphs, or to identify headings.
- Avoid less common ASCII characters such as copyright and TM since many are not supported by all mail clients.
- Include a link to the online version.
There are also some pitfalls to avoid:
- Take care when using ALLCAPS as many spam filters do not like them.
- Make sure that the content is similar to the HTML version – don’t just add text to up the character count. In particular, if you include any links (see below) the links and especially the domains should be the same as in the HTML version.
- Don’t be tempted to leave the header and footer out of the text version. This is still a marketing email and you will need to include your company information, unsubscribe link, etc.
- Don’t be lazy and use the same standard text version for all emails – spam filters will pick up on this.
To sum up, if you can take the time to create a quality text version, do so. If you cannot, then at least take advantage of the simple functionality offered by Emarsys for auto-generating it (see below). This might not look particularly attractive to readers, but they will at least help your deliverability.
The following online resources can help you understand multipart messages better:
- https://wordtothewise.com/blog/ is a good blog for everyone that is dealing with deliverability.
- http://www.w3.org/Protocols/rfc1341/7_2_Multipart.html is the RFC that explains multipart messages.