Ever had your newsletters get cut off by the 'This message has only partially downloaded' prompt in iOS Mail? Preventing it from appearing may be a mix of keeping your message short and sweet, then simply trial and error.
If you test your email designs on an iOS device like the iPhone or iPad, you've likely seen the following message:
While having your messages temporarily truncated may appear to be a mild annoyance, it does bring with it a silent issue - unless the email is fully downloaded, the open may not be recorded. While Email on Acid wrote an authoritative article on this less than a year ago, it seems that conditions have changed since then.
What triggers this message?
From our tests, we were able to reliably trigger this message by:
Making the HTML file size greater than 15kb. This total does not include images or the plain-text version, both of which seem to have no impact on whether this message gets triggered.
Downloading the message over cellular data, not WiFi. In a way, this is to be expected, given the cost of data in some countries.
As you can imagine, it's fairly easy to make the 'partially downloaded' message display - all that's required is a fairly-long newsletter with a comprehensive stylesheet for good measure. Unlike EoA's determination that only POP mailboxes are affected, we found that this could be reliably replicated in clients using IMAP, too.
In addition, we tested on iPhones running iOS 5 and iOS 6 and found that both truncated messages that exceeded 15kb and were accessed over cellular data.
Trial, error and sometimes even a fix
What makes this issue so mysterious is that it's sometimes possible to send HTML file sizes that are larger than the prescribed 15kb limit without triggering this message. In one test, we were able to dismiss the message repeatedly by removing the opening <body> tag. However, when this fix was applied to another newsletter, the message appeared, much to our chagrin. While EoA suggests this can be remedied by ensuring that there are more than 1,019 characters before the closing </head> tag, in the case of our successful <body> tag tests, we were able to get away with far less.
To avoid this message, your safest bet is to keep all email newsletters short and sweet, thus steering well clear of the 15kb danger zone, wile keeping in mind that inlining your CSS may also bump up the file size. Removing line breaks using a tool like HTML Minifier can also help keep file sizes down, but it will also make your code relatively unmanageable, too.
But at the end of the day, if the upper portion of your email is engaging, it's likely that folks who come across this message will choose to download the rest of the newsletter. So if anything, the best remedy is to ensure your content is interesting and relevant enough to make readers want to read more.
Have you had your email newsletters truncated? Is there another workaround? Let us know in the comments below.