1. Relaying denied. IP name lookup failed - sendmail error

Problem: Relaying denied. IP name lookup failed [192.168.0.10]

FIX;  

Open  /etc/mail/access

add below line

Connect:192.168 RELAY

save access file

run make all

restart  sendmail

2. how to flush sendmail mail-queue

To flush the mail queue manually in sendmail servers, use

 /usr/sbin/sendmail -q -v