In this article I will show the steps to troubleshoot Synology Mailplus server
SMTP Port Used
Keep the following in mind:
The Synology Mail Plus server uses SMTP port 25 exclusively to negotiate mail transfers with other messaging servers. This port can be configured under service, protocol, SMTP
Under Service, Protocol, Network Interface, the network interface used by Synology MailPlus can be configured .
So open port 25 in firewall rules for this kind of traffic, like with a relay server. Port 587 doesn’t need to open for this kind of traffic.
Access via SSH the NAS
turn on SSH at your own risk and login via the following instruction, click here.
Live view with aggr_maillog
see postfix/smtpd messages
cd /volume1/@MailPlus-Server/aggr_log
sudo tail -f aggr_maillog
TCPDUMP
tcpdump is a data-network packet analyzer computer program that runs under a command line interface. It allows the user to display TCP/IP and other packets being transmitted or received over a network to which the computer is attached.
Install diagnosis tool:
sudo synogear tool
cd /var/packages/DiagnosisTool/target/tool
Run the following command to display the packets and see the communication between the mailservers
sudo ./tcpdump -i eth0 port 25 -v
Postfix queue
Check the deferred queue:
cd /var/spool/postfix/deferred
ls -R
Check incoming emails:
cd /var/spool/postfix/incoming
ls -R
Check corrupted emails:
cd /var/spool/postfix/corrupt
ls -R
Daily report warnings:
- warning: postfix-script
not owned by root: /var/spool/@MailPlus-Server/postfix/.
According to Synology Support those warnings can be safely ignored.
