OK, I am in serious need of assistance here. I suspect that there must be something really stupid and fundamental that I am overlooking. The problem is that I cannot get Outlook 2003 to authenticate to its SMTP server.
I have tried deleting the account and recreating it (shutting Outlook down in between). I have verified that the same settings in a Thunderbird client allow me to send mail without difficulty. I have even installed Outlook on an entirely separate computer and got the same dismal results.
Why Outlook? Well, although I am a Thunderbird user myself my wife uses Outlook. So my most important support client has a problem -- only with sending mail, though, receiving works fine.
Just so you can visually verify that I haven't done anything stupid, here are screen shots of the relevant dialogs. I have even set up a local printing SMTP proxy to verify what's happening! With Thunderbird it clearly shows an AUTH command being send to the server, but with good 'ole Outlook I get what you see below (slightly redacted): straight from EHLO to MAIL with no AUTH at all.
==> (0) '220 holdenwe.user.openhosting.com ESMTP Postfix\r'
<== (0) 'EHLO DoroPC\r' ==> (0) '250-holdenwe.user.openhosting.com\r'
==> (0) '250-PIPELINING\r'
==> (0) '250-SIZE 10240000\r'
==> (0) '250-VRFY\r'
==> (0) '250-ETRN\r'
==> (0) '250-AUTH PLAIN\r'
==> (0) '250-ENHANCEDSTATUSCODES\r'
==> (0) '250-8BITMIME\r'
==> (0) '250 DSN\r'
<== (0) 'MAIL FROM: <email@example.com>\r'
==> (0) '250 2.1.0 Ok\r'
<== (0) 'RCPT TO: <firstname.lastname@example.org>\r'
==> (0) '554 5.7.1 <email@example.com>: Relay access denied\r'
<== (0) 'QUIT\r'
So, if you can tell me what's wrong you may rescue my sanity! Help me, please, this is driving me nuts.