According to Ladaat, the question about the kashrus of electronic cigarettes was recently brought before Rav Moshe Shternbuch.

Compared to regular classic cigarettes, the kashrus issue is different. Regarding cigarettes, the poskim have concluded that no hechsher is needed, as smoking cigarettes is "hana'a", a enjoyable benefit, but is not considered consumption or eating the product. As well, the contents of cigarettes are not considered food or edible items. Vaping with electronic cigarettes, on the other hand, is considered eating, or consuming, because the vaper is ingesting the steam, the vapor, and the majority of the contents of e-cigs are edible items.

So, the question about the kashrut of electronic cigarettes was brought before Rav Shternbuch.

Rav Shternbuch responded saying that electronic cigarettes do need a hechsher. The liquid in the e-cigs contains good flavoring that turns into vapors, and its taste is then felt inside the mouth. According to halacha, this is considered tasting.

This should clear the way for kashrus organizations to get into the e-cig business.

I am not so sure the contents of e-cigs are really so edible. From what I have read a lot of it is made up of chemicals and consuming them individually, not in the form of vaping the mixture, could be unsafe, though I have no personal knowledge of this.

If the poskim determined that cigarettes do not need a hechsher, why do Israeli cigarettes have a hechsher? Is it just marketing, like by bleach and laundry detergent?