Windows Mail not sending

My brother in law has a problem with Windows Mail that has been dragging on for months and I have not been able to solve.

Toshiba laptop Vista Service Pack 2

The problem is that When an email is composed in Windows Mail and the "Send" button pressed, the email goes to the Outbox but then does not get sent. Pressing Send/Receive has no effect. The only way to send the mail is to close Windows Mail and restart it. On restart the mail gets sent immediately and goes to Sent Items. Note that the mail in the Outbox CAN be deleted, unlike other Mail problems I have read about.

Having searched for information in various forums I have tried the following

Deleted the Windows Mail data folder and let Windows mail re-create it. I then start off with a brand new empty Windows Mail - Added an email account - Sent an email - Same result.

Made sure that "Send messages immediately" is ticked
Applied recommended Windows updates
Used WMUtils utilities
As I have now taken the laptop home I am using a different router and different ISP and different SMTP server.

In desperation I installed Mozilla Thunderbird but this failed to import emails and settings even though the folder location is in the standard location.

Any ideas anyone ?

Silly question - is the email account set as default?

does it have have always use a particualr dialup set?

Or how about the anti-virus software, assuming some is installed, sticking a spanner in the works? Most A-V programs will scan incoming and more importantly here outgoing emails. For instance I've seen this sort of problem on systems with PCTools anti-virus installed.
JB

Silly question - is the email account set as default?

Yes (Don't mind silly questions tried everything else)

does it have have always use a particualr dialup set?

No dial ups are set up. Ticking or unticking "Always connect to this account using Local Area Network" has no effect

Antivirus is AVG which works fine on my desktop, however, I have disabled "Check outgoing email" and "Check incoming email" with no effect

In reply to a post by philflyer:

Antivirus is AVG which works fine on my desktop, however, I have disabled "Check outgoing email" and "Check incoming email" with no effect

Disable AVG completely and try again. Is the account setup pop3 or imap?

The account is pop3
How do I completely disable AVG unless I uninstall it?

What I have done this pm is
Uninstalled AVG
Disabled Windows Defender
Run Norton and McAfee removal tool (One of these was installed from new, not sure which)
Created a new user
Under the new user created a new Windows Mail account

Still the same problem

Might be a blind alley, but why not install Windows Live Mail and see if it does the same?

Not sure if the 2 can coexist but WLM is released for Vista.

Solution found at last

I noticed an icon in the system tray which I didn't recognise. It turns out that this is a program called Desktop SMS by ComUnified which integrates with your email program to send texts from your PC (if you pay them). The program was not even configured and yet it was interfering with Windows Mail. As soon as I unticked "link to Outlook" or similiar, mail messages worked as normal.

I am annoyed that I didn't spot this earlier but more annoyed that such a program can sit there and mess things up so badly. I've no idea how it got there. I have been trying to sort this on every visit to my brother in law for months!

Thanks to all that contributed