You will be able to message your connections by finding that specific connection and then clicking on the ellipsis (⋯) - More Menu - on the right-hand side of the connection row and selecting Message option.

You can also send messages to multiple users at the same time by ticking the checkbox on the left-hand side for the connections you wish to message and then clicking on the Message button in the action bar.

Once you click on the Message option/button, a popup will appear presenting the Message box where you will need to enter the message you wish to send. The max number of characters is 2000 and you will be able to view the character counter and the current number of characters used.

Once ready, you just need to click on the Send button and you will be presented with the success toast notification.

In case you sent a message to the specific Connection via LeadDelta, the message icon will turn purple.