Email shows it was sent, but receiver never gets it!

We have several email accounts in our home (mine and my wife).  She has an iPad (apple email app), iPhone (apple email app) and desktop client (Eudora -- yes I know it's an old one, but works find for years on POP) software, all using POP3.

Starting last night, emails that she sent on her iPad or iPhone showed Sent, but in reality, never got there.  I did multiple tests of "sending" from iPhone and iPad to her own email address as well as mine.  Nothing.  Yet they were present in her "sent" folder.

I called Cox this morning, then Level 1, then Level 2.  Level 2 said "Yes we are having a problem with some accounts.  Wait 24 to 48 hours for resolution/fix".  Is it just me or is anyone else having this problem?  Very frustrating.

My emails (iPad, iPhone, and desktop Outlook 365) all work fine.  But as you can imagine when you "think" an email was sent, you think it was really sent, not hung up somewhere.  Can anyone shed anymore light on this?  (I know Cox made some major changes in email settings requirements last month, and I reviewed them again, unless something else has changed.)

PLEASE, what is going on?  Thanks!