To reduce bounce rates and the chances of your emails landing in contacts' spam folder, you'll need to add DKIM and SPF records in your DNS Settings.
You can take a look at the links below for Gmail and Outlook for help on how to add these records.
Gmail:
Enhance security for outgoing email (DKIM)
Authorize email senders with SPF
Outlook:
Set up SPF in Office 365 to help prevent spoofing
Use DKIM to validate outbound email sent from your custom domain in Office 365