Send an announcement suddenly began failing - Yahoo & Hotmail Related

[tombstone66]

I WAS using MF 1.1.13 when I encountered this error however I did just update to SMF 1.1.14.  Still received the same error following the update.

I have my mail server configured in Server Settings-Feature Configuration for sendmail (PHP) and have not had any trouble in the past year or two until yesterday.  I haven't changed a thing.

When I post a topic on the board and use the "Send an announcement", I get a 500 Internal Server Error

The Error log shows the following

2: mail() [<a href='function.mail'>function.mail</a>]: Failed to connect to mailserver at "relay-hosting.secureserver.net" port 25, verify your "SMTP" and "smtp_port" setting in php.ini or use ini_set()
File: D:\Hosting\5006776\html\forum\Sources\Subs-Post.php
Line: 661

Curiously, I also began receiving errors that emails to Yahoo addresses had failed.  I get one of these errors prior to each iteration of the above error message.  This seemed odd to me and seems to indicate that the sendmail function actually DID do something,

This error message simply states Unable to send mail to the email address '[email protected]

This also happens with Hotmail addresses as well.  I've poked around the support forum but have had no luck in finding any helpful clues.

Any help would be appreciated.

Tombstone
www.cvmaflorida.org

[tombstone66]

UPDATE

The "Send Announcement" feature seems to work when I choose certain groups of board members but when including certain other groups or all groups, I receive the following ERROR message (which is ALWAYS preceded by another ERROR message regarding failure to sent a message to a Yahoo.com or Hotmail.com recipient.)

2: mail() [<a href='function.mail'>function.mail</a>]: Failed to connect to mailserver at "relay-hosting.secureserver.net" port 25, verify your "SMTP" and "smtp_port" setting in php.ini or use ini_set()
File: D:\Hosting\5006776\html\forum\Sources\Subs-Post.php
Line: 661

Tombstone
www.cvmaflorida.org

[tombstone66]

ANOTHER UPDATE

I've confirmed that the SMF's email function works because if I use the "Send this topic" function to send the topic to a NON Yahoo or Hotmail address, it works fine AND if I send it to someone on the Yahoo or Hotmail domains, it works fine and the email is delivered to the recipients email INBOX. 

The conclusion is therefore that the failure is somehow tied to the "Announce Topic" function and possibly Yahoo and Hotmail.

Anyone?