Linc: Thanks - I suspected that, but thought there maybe a hidden clue to my current inability to send email. Please note, that was an anomoly for a couple of weeks with that one ISP & not with any other - I said it may be a red herring & it seems it is.
Munas: I only have one email account. I also do not have any other devices (iphone, iPad, Apple laptop) just my iMac. Plain and simple, no complications. So I have one mailbox which has one Inbox, one Drafts folder, one Sent ffolder & one Trash folder.
I have emptied out all four folders. I am still receiving mail, which I am deleteing after reading. I can't answer them because I cannot send.
I do not have any saved email file folders.
I have no router, I have no others sharing my WiFi high speed Internet. My WiFI needs a password so no outsiders are using it.
I have no Firewalls or protection other than what may reside in the standard Apple Mail that is embodied in my 10.8.2 Montain Lion OSX software. My software is up to date.
My server has verified all my settings are correct to enable me to send & receive emails. Since I could not send emails despite everything being correct, with the server's direction & consent changed the port to 110. That change did not resolve the "inability to send" issue.