Not sure what you’re asking.
- Yes you would need to re-verify the domain with the client’s account, so that they can use it, this is a TXT record
- Some other site settings will likely need to be re-set… Apps / integrations, maybe reCAPTCHA, maybe 301 redirects.
- Webflow doesn’t provide any email services. You’d sort that separately.
It’s not much downtime to do the transfer and re-verification of the domain, just do it during a low traffic period.