Again I mean I want to send 50 emails to 50 subscribers per day. What is the maximum amount of emails I can send a day and should keep in mind when sending to my subscribers?
Your question does not make any sense... If you send an email out on your newsletter then send it to everyone on your list... Why would you want to send it bit by bit over many days?
By the way what are you using for your autoresponder? Is it an email marketing service provider such as aweber, mailchimp etc - you pay per month for the total number of subscribers and not number of emails...
If its completely self hosted solution then its a matter with the web host e.g. x amount per hour... If you exceed that amount then it rolls over into a queue... Typically that's around few thousand per hour - so even that should not raise any issues with sending more than 50 emails...
If its a hybrid solution of using an SMTP service such as Amazon SES then you're looking at no restrictions as its free upto 10,000 and after that its around $0.10 per thousand.