How can I modify browser to control DOM of any loaded document?

I want to login in gmail account automatically. Then want to create a mail through contents of a text file. Then select Email addresses from Database one by one and send mail through GMail account and everything should be absolutely automatic.

I mean. I have a list of thousands of emails and I want to send all of them a personalized mail through GMail account. But I don't want to create 500 mails per day manually. I want to do this thing automatically. So I think, I should create a system which have following Algorithm.

1 Automatically login to GMail account.

2 Automatically compose a new mail.

3 Automatically sele开发者_StackOverflow社区ct an email address from my database.

4 Automatically Paste content in composing mail.

5 Automatically click on the send button to send the mail

6 Again automatically follow steps 2 to 6 until all emails are not sent.

I can do all these things if I can control the Web Browser because without controlling the browser, I can't do all these things. I want to know, How can I achieve this and through which language?

Automated testing tools can do the trick. Try WatIn. WebLoad could also work. You can automate access to a site and the clicks with it. You should be able to leverage that to send out your emails.