Can I send messages to friends who do not have CoverMe?

Absolutely yes.
CoverMe allows its users to send messages to both CoverMe users and non-CoverMe users. Also, its users are able to receive messages from anyone on CoverMe.

Moreover, the messages between CoverMe users and the other side are transmitted through an encrypted tunnel to stop them being tracked or monitored by third parties or individuals. CoverMe provides secure features, self-destruct for example, to its users to protect their messages from being abused or eavesdropped.

In one word, CoverMe not only allows its users to send messages to anyone no matter they’re using CoverMe or not but also safeguard their privacy.