For those inevitable times when you're too busy to develop on-the-fly content for your e-newsletters, it's not a bad idea to have a content reserve. When you're in a tight spot, it's nice to be able to plug in some pre-packaged material so you can keep your mailings on track. Your emergency stash can contain anything from whole articles to whole newsletters.
For those who choose to create their newsletters in advance, MNB has a neat tool called Auto Series which will send your pre-created newsletters at specified intervals. To borrow a slogan from a popular "as seen on TV" rotisserie company, you just "set it and forget it!" It really is a beautiful thing.
Just remember, reserves get depleted if too often relied upon, so use your stash sparingly. Furthermore, don't use your reserve as an excuse to avoid developing timely content. Reserve articles are usually quite general insomuch as although they are relevant, they tend to lack a current, newsworthy element. This is why it's important to allow time to add in at least a pinch of up-to-the-minute content in every email you send.