I have hired an email server for my business promotion but I am not able to send lakhs of mails to my customers. My email server provider says "No technical problem from our end, please check your mailing list and email content".But I do not understand what to do with server so I can get fast email delivery.

This is really a question for your e-mail servers technical support people as it is unclear what you are trying to do.
They have already given you some things to check.