Your first message only indicates your local sendmail MTA accepting the message for local processing. The second message is about failing to connect to
mail.protonmail.ch which is the server indicated by the primary MX record for
protonmail.com. That would be the next hop on the mail's path to the destination.
Your VPS provider might be required by local regulating authorities to restrict outgoing unauthenticated SMTP connections in port 25 to the VPS provider's local SMTP servers only, to make sure spammers and email-sending malware can be detected and their traffic stopped as near the source as possible.
In that case, you might have to specify the appropriate outgoing email server as your "smarthost" through which all outgoing email will be sent. This can be done by putting something like this in your
and then regenerating your
sendmail.cf (often with
cd /etc/mail; make).
You should also be aware of a thing called greylisting: mail servers may, when receiving a connection from a previously unknown source, initially reject the connection/message but remember the IP address it was coming from. A legitimate mail server will try again a few minutes later and will then be accepted; a spammer/malware might just skip to an easier target. After submitting a few valid mail messages in this delayed way, the remote mail server may omit the delay mechanism.