SMTP please help


I am sitting on the edge of my chair.
I do not know why, but I can not get anything with SMTP to work, send emails.

I thought it was the third party software, so I tried another and another and another and …

Well either all programs/scripts are very very bad
or I am doing something very stupid everytime again
or … I don’t know.

I know the SMTP settings, I have Thunderbird setup no problems

With any other third party software, that needs to be installed online, like an ecards or newsletter scripts it will just NOT work.
I even tried using the gmail smtp but also no luck.

I know the header email needs to be from a domain registered, but if I fill in the SMTP in the third party scripts, I still can NOT send out emails which come from e.g. gmail as sender.
Well an ecard scripts has people wanting to send a card and use gmail, hotmail or which ever.

I also know the ONLY problem is the HEADER email, because if I install the script(s) on my other server (non-DH) ALL works with out a hitch, but then they just allow sendmail, I think it is called.

So HOW do I get all this to work on DH?
I have been with them for over 7 years, but this is starting to really frustrated me and for the firsttime in 7 years I am thinking of leaving, but rather not.

I always get the same error 1 or 3 times: SMTP error. Can not connect to SMTP Host
I know not a useful error.

I downloaded the latest phpMailer and as far as I can tell I made the correct changes also in there. Tried a dozen or more different settings.

Best, Ron