Failure to Send -- Again & Again

Question

Far too frequently than should be, Mail is simply refusing to Send mail. Then the message winds up in the Outbox. I try to use message>send again, and it still doesn't work.
This machine is connected to a cox.net server via cable modem, and the configuration for the account is working. I just sent one message to a yahoogroup, and it worked just fine. Several other messages are all hung up in the Outbox for no apparent reason.
This is something that has happened before with an Earthlink and even a .Mac account.
In the past I've been forced to delete the message, then turn off the machine, then start over and MAYBE Mail works.
Any help or suggestions would be welcome. Thank you.
Dave Clark
<[email protected]>
<[email protected]>
iMac Intel & MacBookPro Intel   Mac OS X (10.4.9)  

Answer 1

This problem is continuing.
Yesterday afternoon, I prepared and sent a message from the MBP "using" one of my accounts. That is, when composing a message Mail asks which account you want to use and I entered that account name. This causes the recipient to believe that the message came from me at a certain business.
Then, this morning I discovered that the message had not been sent. Mail puts the msg in the outbox and has a pop-up that tells you to select another server, and only sometimes will that other server work.
Just now from a different machine (the iMac) I set my .Mac smtp to port 587, and was able to send a message without any problem. But, both of these machines are physically attached to the Internet via Cox.net cable modems, so Cox.net messages should have no problem being sent.
In my opinion, none of this should be happening. But short of switching to webmail, there does not seem to be any solution. Over the past few months, I've made repeated calls to Apple and both my ISPs. The webhosting company for my office even examined my Mail settings and for a while it worked OK.
I suspect part of the reason for the continuous problem is that I take the MBP and use it both at my office (served by AT&T internet, with another company providing Webhosting), and then at home (physically served by Cox.net cable internet but through a Belkin wireless router to the iMac -- which stays connected all the time to the cox.net cable modem). My guess is that this confuses the MBP, and it somehow infects the iMac.
(BTW, problems were even worse using Eudora, which is why I switched to Mail on the Macs. I never could get Eudora to work on the MBP here at home, only at the office.)
Dave Clark
www.clarklawfirm.com
web.mac.com/dave28c/
home.earthlink.net/~dc1999/