Why are Yahoo and Gmail blacklisting DigitalOcean IPs?

I have experienced the following situations:

1. I have been using 2 DO droplets as personal VPN when working from public hotspots. Well, I found that gmail claims the IPs to be from Iran and from Indonesia, (when they belong to NYC and SF datacenters), and I am blocked access to such services as adsense and analytics. Since google is supposed to know better, this incongruency appears to me to be on purpose, not by mistake.

2. I have used a third droples for two months to host a couple of development sites. Wel, yahoo blocks all email from this server with the message:

“All messages from xx.xx.xx.xx will be permanently deferred; Retrying will NOT succeed”

I have added dkim and spf records for the domain, and contacted yahoo support, but to no avail. I am quite sure my server has not been sending bulk email, but fearing the server was compromised, I then spun another droplet and migrated the domain to the new address. But even the first email I sent from the fresh new IP was immediately blocked by yahoo. At least gmail lets the emails through, so yahoo’s position appears more damaging to me (but even being falsely labeled as connecting from Iran or Indonesia can be damaging - no disrespect meant to those two countries).