My job is to send 300 emails per day through Yahoo mail. I could not send even 50 emails per day as some problem comes and obstructs in sending emails. SMPT may be not properly connected to my computer and I want to set it, but I donot know how to operate it exactly in my computer. Please help me in doing so.

Check your configuration in your email client. Also sending 300 emails a day should raise some scrutiny through Yahoo. Not knowing what you are doing it sounds like a email marketing so there is a chance it may trigger Yahoo's anti spamming software.
More info on what type of emails what the subject lines are and how addressies are determined may shed some light on the problem