Hi Koteswar,
1.First create a Z table to maintain the mail ID(Finance Person) of the person with the required parameter.
2.then create a Z program , which will send Mail to the person mentioned in the above Z table when Credit block is removed for a SO.speak to your ABAPer they might do this needful.
you can schedule the batch job for this also .
3.once it is Done then you can see it in SOST transaction.
Hope this helps to you
regards
Sundar