Is it possible that what those domains have in common with yours isn't a DigitalOcean IP, but a current or past Plesk installation? It's a long shot, but that's a surprising issue that we've encountered before with expiration e-mails:
Is it possible that what those domains have in common with yours isn't a DigitalOcean IP, but a current or past Plesk installation? It's a long shot, but that's a surprising issue that we've encountered before with expiration e-mails: