SBS - Certificate Expiry Warning

try these commands:

1. to get the thumbprint type: Get-ExchangeCertificate -domain "servername" | fl
2. thumbprint in step 1 enter in step 3.
3. type: Get-ExchangeCertificate -thumbprint "2FB28F5075EFE9B30A8F8458DED0A137629F62D7" | New-ExchangeCertificate
4. you'll confirm "overwrite existing default SMTP certificate, take the new thumbprint and enter in step 5
5. Enable-ExchangeCertificate -thumbprint "FB5AECA6B39816F 02B3245BD1D953934HD8H730F" -services IIS

Where do i type these commands?
Do I use the CMD (command prompt)?

exchange Management Shell (powershell)

I did that acutaly and I typed:

Get-ExchangeCertificate -domain "MainServer" | fl       <--- there was no return vale

Get-ExchangeCertificate -thumbprint "2FB28F5075EFE9B30A8F8458DED0A137629F62D7" | New-ExchangeCertificate           <--- there was no return vale

Enable-ExchangeCertificate -thumbprint "FB5AECA6B39816F 02B3245BD1D953934HD8H730F"  
<-- when i put this line it askes for service ... I put      IIS   and it is return with an error

It's not necessary or desirable to do this through the exchange shell on SBS2008.  Go to SBS Console > Network > Connectivity  and run the 'Add a Trusted Certificate Wizard'.

I believe I have to buy the Certificate!!!
Where can I buy it????

Remember I'm new at this your help is greatly appreciated

I will keep you posted as soon as I figure it out lol