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None working mail after saving A records in the DNS

Hi I’m working on E-commerce for a client that already have a domain name on GoDaddy, so I just followed the step to add a custom domain on Webflow
After that they told me to save 2 A records and 1 CNAME on my domain’s DNS provider, I saved the A records but couldn’t put the CNAME because of GoDaddy policy terms.
Then the client call me because he couldn’t send and receive mail. So I deleted my changes and call GoDaddy who told me that’s normal I don’t have MX records on the DNS.
I didn’t touch the MX so how they could have disappear and how I can make sure that if I put them it’ll work ?
The mail service is Microsoft 365 and the hosting is by OVH.

Thanks for the help