Cox email not being delivered to Protonmail
My Cox emails are being bounced back when sent to friends with Protonmail. All other recipients receive the emails with no issue and my Cox account can receive emails from Protonmail, just outgoing emails are not delivered. Also, Protonmail support has looked into this and they say they see no issues on why Cox domain is bouncing back emails.
This is the message I get after a few days:
From: Mail Administrator <Postmaster@cox.net>
Date: July 2, 2018 at 7:23:06 PM CDT
To: [my email account]
Subject: Mail System Error - Returned Mail Reply-To: <Postmaster@cox.net>
Most likely there is a network problem that prevented delivery, but it is also possible that the computer is turned off, or does not have a mail system running right now. Your message was not delivered within 4 days and 0 hours. Host protonmail.com is not responding.
The following recipients did not receive this message: [recipient's email address]
Please reply to <Postmaster@cox.net> if you feel this message to be in error.
I have forwarded this to postmaster@cox.net, but I feel that's just a generic message. Any ideas?