Domain Health Checker Errors

I checked my domain in mxtoolbox and found following errors/warnings:

1. dmarc Missing or Invalid Record
2. https The Certificate is invalid
3. smtp Reverse DNS does not match SMTP Banner
4. dns At least one name server failed to respond in a timely manner
5. dns SOA Expire Value out of recommended range

I added a txt record in DNS zone for as "_dmarc" and checked it

nslookup -query=txt _dmarc.mydomain.com

its showing our server IP

Please advise how can I fix all these errors or warnings?

Best regards