Go for the click, not the read
When you have a lot to say, you tend to say a lot but do you save it all up and say it all in one go?
If you did that to a person while at work, how long will they last before they had to stop you because they had to get back to work?
The same thing applies to email.
Email is the shop window to the web-site where you tempt them in except it’s at your front door/inbox.
If you put all of your wares in the window they would only need to walk in to the shop if they wanted what was in the window.
But because your shop/web-site has even more great things to spend money on inside, you add content to the email to entice them in so they walk in the door, where there is a whole store of products that people can touch and try on.
A web-site is capable of far more dynamic experiences than an email, the page space is bigger, you can make images move, include videos, allow people to socially share it, leave comment and more.
Send more, say less
Everyone is busy, from the success of Twitter we can safely assume that a web-users’ attention span is tiny. All people get is a subject line and a link to click from Twitter. While an email can give more, it can also give too much and people may get bored a tune out.
If someone sees that the scroll bar on the right of the window is tiny when they open your email, they will know it is a long email. They are likely to decide to read it later when they have the time and then probably not get around to it.
Then over time, they will expect the email to be long and knowing that they will need to allocate more time than they have now to read it, they’ll make a filter and put your emails in to a folder and slowly fade out of your openers.
If you have a lot to say send more frequently but with less content.
Try sending bi-weekly or weekly rather than monthly and even offer people the choice to have a weekly email or a monthly digest.
Segment out the people who are not opening your monthly emails and send them two articles a day for a month, see if that wakes them up.