For eSignature I speculated on Twitter https://twitter.com/sytses/status/1319360157113970688?s=21
For CDNs we switched from Fastly to Cloudflare because we needed support for SSH (port 22)
And for email sending I think you want multiple providers so you have a hot one (already know on the internet to send a large volume of mail in your name) in cause a provider has problems with delivery.