I have one person receiving a lot of non deliverable email messages.
They have been blocked via Barracuda and UCEProtect.
I created a block rule for Port 25 in my Cisco Router. This is what is being blocked.
The MAC address is that of the router and the server.
[ACCESS_RULE]: IN=eth0 OUT= MAC=50:3d:e5:a2:40:d4:00:13:20:5c:d5:e7:08:00 SRC=192.x.x.10 DST=217.x.x.23 LEN=60 TOS=0x00 PREC=0x00 TTL=64 ID=49012 DF PROTO=TCP SPT=35962 DPT=25 WINDOW=5840 RES=0x00 SYN URGP=0
How can I troubleshoot this to determine where the issue is coming from. No changes on the server. This started about a week ago.