Can't send VSNL outgoing email using GTPL connection as my ISP.

hi
I am having email account of VSNL and using GTPL connection as my ISP. I am able to receive incoming mails but not able to send mails (Outlook Express). Please anybody help me out with it.

Also :
Using Reliance broadband connection as my ISP. I am able to receive incoming mails but not able to send mails (Outlook Express). Please anybody help me out with it.

May be VSNL has set that SMTP is only allowed if its through their own network. Also, incoming connections are not really allowed in such cases .