The mail messages will come from a single IP address that's managed by the mailing service sendgrid. What's happened is that the sendgrid mail server will have had some difficulty or another in delivering mail to your email address. So, your email address is placed on a suppression list and sendgrid will stop sending. Despite eon's mail being sent to sendgrid to pass on to you the stop on sending will mean you receive nothing.
The solution is to ask the eon customer service team to ask their email admins to remove your email address from the sendgrid suppression list. Then you'll be back in action receiving eon's mail.
Sendgrid suppression list
