CDO.MESSAGE.1 The transport failed to connect to the server

Question

I know there are several threads related to this, but none of them answered my question.

Mere's the code (VBScript):

With cdomsg.Configuration.Fields
  .Item("http://schemas.microsoft.com/cdo/configuration/sendusing") = 2 'NTLM method
  .Item("http://schemas.microsoft.com/cdo/configuration/smtpserver") = "smtp.gmail.com"
  .Item("http://schemas.microsoft.com/cdo/configuration/smptserverport") = 587
  .Item("http://schemas.microsoft.com/cdo/configuration/smtpauthenticate") = 1
  .Item("http://schemas.microsoft.com/cdo/configuration/smtpusessl") = True
  .Item("http://schemas.microsoft.com/cdo/configuration/smtpconnectiontimeout") = 60
  .Item("http://schemas.microsoft.com/cdo/configuration/sendusername") = "robot@gmail.com"
  .Item("http://schemas.microsoft.com/cdo/configuration/sendpassword") = "pass"
  .Update
End With

With that code, everything works just fine with my computer. But on other PCs this error appears:

CDO.MESSAGE.1 The transport failed to connect to the server.

Things that I have done:

1. Checking via telnet port 25, 465, 587. Only 465 didn't work.
2. Changing the port to 465, 25, 587.
3. exclude my .exe (this program) in AntiVirus.

I have those smtpusessl, autheticate, etc.

I have no clue what to do and to check anymore. Is it possible the system blocks this kind activity?

Answer 1

I have found the cause behind of this issue, it seems the ISP causes this. I have tried in more than 2 ISP in more than 3 computer let's say A, B, C. A and B works fine with the same code but every computer with C provider error. using port 587 or 465 both work fine. I dont really understand about this port but both work fine.