Not the SSL certificate for your domain, which Fastmail will acquire with or without your prior knowledge or consent, and to which you have no access or control.
They can't request a certificate unless you already pointed your domain to their servers. So if you're already doing that for HTTP, requesting an ssl cert so they can enable HTTPS on it is a perfectly valid request... especially when browsers are starting to mark all HTTP sites as insecure.
They can't request a certificate unless you already pointed your domain to their servers. So if you're already doing that for HTTP, requesting an ssl cert so they can enable HTTPS on it is a perfectly valid request... especially when browsers are starting to mark all HTTP sites as insecure.