Connecting SharePoint 2013 to exchange online service accounts.

We migrated service accounts from exchange 2016 on-premises to Exchange online, the issue is that while using SharePoint 2013 on-premises, some notifications get stuck in the queue.

There are already connectors in place, so I didn't have to create any. The issue is;

1. How to ensure that your on-premises SharePoint 2013 environment can send emails using service accounts that have been migrated to Exchange Online without being intermittent.
2. Any other applications on-premises can communicate with service accounts without affecting business continuity with the intermittency.

Thanks.