Thanks be to you, Rusty and Jose; One or all of you (apparently) hit the nail on the head.
Prior to posting my problem message, I had called my ISP and they assured me that everthing was ok. (and like someone said, they told me that I probably had things set up incorrectly)...
Or, as rusty and Jose suggested that I change local domain from mail.hopestar-b-cohiper.com to just plain hopestar-b-cohiper.com; also I changed my SMTP server address from mailhost.cin.net to 204.120.48.3 as suggested by you Rick.
Whether it was one of the things I did above or my ISP did, I do not know, but now everything with my E-mail appears to be working ok.
