"messaging" Implies that these notices travel from A to B likely in your own network, but you added "secure". This suggests the network itself is only password protected and is a compromise - or two? - away from revealing what is being sent. The purpose of encryption is to limit the damage should eavesdropping of the network occurs.

Ex: Your routers, switches, RAID storage etc. are not immune to rootkits. However, if your message from A to B is encrypted and only decrypted locally by B, you've limited the exposure of this information.