This work explores the properties of different output modalities as notification mechanisms in the context of messaging. In particular, the olfactory (smell) modality is introduced as a potential alternative to visual and auditory modalities for providing messaging notifications. An experiment was performed to compare these modalities as secondary display mechanisms used to deliver notifications to users working on a cognitively engaging primary task. It was verified that the disruptiveness and effectiveness of notifications varied with the notification modality. The olfactory modality was shown to be less effective in delivering notifications than the other modalities, but produced a less disruptive effect on user engagement in the primary task. Our results serve as a starting point for future research into the use of olfactory notification in messaging systems. Categories and Subject Descriptors H.5.1 [Information Interfaces and Presentation]: Multimedia Information Syst...