If the majority of your employees are on Slack and they don't check emails often, then Slack becomes a better way to facilitate communication.
Through Slack, you will receive notification about 1-on-1 meetings and Goals.
Go to the 'Settings' option under your profile. Then go to 'Slack Integration' from the left panel and click on 'Add to Slack'.

Here's a list of notifications and reminders that you'll receive on Slack once it's integrated with Peoplebox:
Add talking points reminder for upcoming 1-on-1 meetings
Before any upcoming 1-on-1 meetings, Peoplebox will remind you through Slack to add talking points for that meetingAction item reminder
When you set a reminder for your action items, you will be notified on Slack when its dueGoal assignment
If someone assigns you as the owner of a goal, you will immediately receive a notification on SlackWeekly goal(s) check-in
Every Tuesday, you will be notified on Slack to update the progress of your goal(s).
Note: If you integrate Slack with Peoplebox for any one feature, it will be automatically integrated with other features as well.