Just an update. Looking around, it appears that Everyone.net announced this change in January of this year via email to account holders. This was the announcement I found:
EVERYONE.NET CHANGE OF PUBLISHER MAIL SERVICE
Dear Publisher Mail Partner,
Upon final review, Everyone.net will be ending access for free web mail accounts to the Publisher Mail (formerly Sponsored Mail) service on Thursday, March 23rd, 2017. Subscribers to Mail Plus Total Protection will continue to have access and will not be impacted. Free Publisher Mail users will be given the option to subscribe to Mail Plus Total Protection to continue using their email service.
Prior to this on Thursday, February 23rd, 2017 free Publisher Mail users will have their ability to send email through web mail disabled. Free Publisher Mail users will be notified of the upcoming changes through web mail. The benefits of Mail Plus Total Protection include:
2GB mail storage
Advertisement-free web mail
POP, IMAP, SMTP, and mobile access
one_mobile service to sync email, calendar, and contacts
Email-based technical support
This change is part of our ongoing efforts to reduce email abuse and improve security. Thank you for choosing Everyone.net.
The Everyone.net Support Team