I am also looking for a similar service? i need to send atleast 15k emails every week. can you advice some cheap smtp service
Mandrill is free for 12k emails per month, then $0.20 per thousand above that up to a million mails a month.
15k per week = about 65k per month, so you'd have to pay for 53k of those. Cost: just over $10 per month.
That's a good price for that kind of mail volume, and Mandrill's service is excellent. The genius of the way their feature is set up is that the number of e-mails you can send per hour is calculated by a combination of: (i) how many you are actually sending (so that you can ramp up to a big number only if you need it), and (ii) how low your bounce-counts are. Sellers who are careful not to send spam will be able to use Mandrill to send large volumes, spammers will find themselves throttled and so Mandrill's reputation is unharmed.
That makes them a good bulk mailer, combined with excellent customisation / reporting features.