Frontier has also contracted with Yahoo Mail, and Yahoo is refusing our mail for Frontier:

May 3 15:00:57 mail postfix/smtp[20420]: E17491994: to=<REDACTED@frontier.com>, relay=mta7.am0.yahoodns.net[63.250.192.45]:25, delay=150175, delays=150143/0/32/0.01, dsn=4.7.1, status=deferred (host mta7.am0.yahoodns.net[63.250.192.45] said: 421 4.7.1 [TS03] All messages from 204.122.16.4 will be permanently deferred; Retrying will NOT succeed. See http://postmaster.yahoo.com/421-ts03.html (in reply to MAIL FROM command))

That link redirects to: https://help.yahoo.com/kb/postmaster421-ts03.html

Which provides the helpful information:

Sorry, the page you requested was not found.

We suggest you visit Help Central

… Help Central has not been the least bit helpful.  I would ask people to see this article:

http://blog.mailermailer.com/industry-news/yahoo-blocking-legitimate-email

We haven’t had any more problems with compromised accounts since the Thursday before Last, April 24th, yet Yahoo continues to block our e-mail, and since they are now providing e-mail for ATT/SBC Global and Frontier, this affects those providers as well.

I’d ask you folks, if you have a Yahoo, ATT/SBC Global, or Frontier account, please generate a support ticket and/or complaint there.  Please spread the word about Yahoo’s practices.  There has to be a better provider ATT/SBC Global and Frontier could contract with and actually get functional e-mail for their customers.