Does the high ODS effect pop3 client receive big attachment slowly

we have three internet domain.we did global domain.etc,x@A.com,b@B.com,c@C.com.every internet domain have its own mail Domino server.we update the mail server ods of C.com to ods(48).we found the pop3 users recive slowly of the 4-5M mail with big attachment(not too big,about 5-6M),and other server of ods(43) receive is OK.we use outlook2003 to receive the mails from Domino server.

Does the high ods effect the pop3 users?how to find reasons and slove it ?

thks for every comments.