Problem in sending mail on the server

Hello,

Unable to solve a problem

when the administrator of the forum trying to send email to his members most of the members they did not get emails

When he send to the members of the forum only the first 100 or 200 members they get the emails ( Messages) on them inbox but the other the did not get anythings

The number of members of his forum Reach to 5000 Members

I do not know where the problem occurred
can any one help


regards,

 

thanks for reply

no i did not receiv also i chack the log in
/var/log/exim_mainlog
but i did not find any thing like reject or error