I have a web server running CentOS and a separate mail server running Microsoft Exchange. I have the web server connecting to the mail server via SMTP on port 587 to send emails.
Sometimes the connection to the mail server refuses, but it's rare. Could an intermittent failure be related to port settings? I would have thought it's all or nothing.
For the CentOS web server, what rules should I be looking to configure in the iptables if any? Do I need to add an entry for port 587 on this server? Or do I just need to allow incoming connections on the mail server for 587?
Thanks in advance.
You don't need to set up any iptables rules on your webserver, since outgoing connections are allowed by default. Your occasional drops won't have anything to do with the webserver's firewall, so you'll want to look at tuning your Exchange server, if the error is impactful enough to worry about it.
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I have a VM instance on Google Compute Engine, which is running Windows Server 2012 R2. I have my Apache web server, PHP, MySQL, FTP, and various other things running great, easily accessible from the world. I installed MDaemon Messaging Server (Alt-N's email server), which I had on my old physical box for years. I am able to use port 110 just fine, but I simply cannot get SMTP to work. Yes, I'm well aware of (Compute Engine's Blocked SMTP Ports). Knowing these blocked google ports, I would like to choose port 2525 as Mdaemon's SMTP port. I added firewall rules on the server to allow it, and I added the Compute Engine Network port exceptions as well, and of course changed the Mdaemon's server settings for 2525. I still cannot send email. Hell, I even tried port 2626 and nadda.
I understand I could sign up through google's recommended "sendgrid" that would force me to use mail.sendgrid.com, port 2525, and have a maximum of 25,000 per month limit (on free sendgrid account), but I personally think it's ridiculous needing to sign up and have limits on email when I paid $2,400 for Mdaemon email server. I should be able to use my own domain's mail.mydomain.com and authenticate through MY email server, not sendgrid's.
Is there something simple I'm missing to be able to use my own email server software on my google compute engine VM instance? Or is it just fact that this is the right I give up by choosing google's cloud server services?
SMTP server, in your case MDaemon, sends all outbound emails directly to the recipient's mail servers on their inbound SMTP port which is 25. This is the port you will need to configure on your MDaemon's SMTP outbound port setting. So changing it to 2525 or 2626 won't help because recipient's SMTP servers usually do not listen on those ports.
As you also mentioned all outgoing traffic to port 25 (SMTP) is blocked on Compute Engine. Therefore you'll need to configure a smart host for your MDaemon message routing which listens on a non-blocked port. This is something like using a third party service (e.g. SendGrid).
I have a web app that sends email via SMTP (Gmail, Zoho Mail servers). The thing is, the email sending works in my localhost but not on my VPS (using WHM).
I contacted support and the guy replied:
If your VPS has ConfigServer Firewall (CSF) installed then this would
most likely be causing the problem. As it is working on localhost but
not externally this certainly sounds like it might be the case. You
will need to review the firewall configuration on the VPS and ensure
hose ports are allowed outbound.
But when it comes to server management and configuration, I'm totally lost. I did check the CSF settings page on WHM but not sure where to start.
Any recommendation or solution would be appreciated.
You have to allow outgoing traffic to ports 25, 465, 587 and in the case of Mandrill 2525 as will. You should actually be fine enabling only the one you will connect to. So:
sudo vim /etc/csf/csf.conf
add 25,2525,465,587 to TCP_OUT, and to TCP6_OUT if you use IPv6.
You might also need to remove that ports from SMTP_PORTS if you have SMTP_BLOCK enabled (if it is set to 1).
Source: https://community.centminmod.com/threads/csf-firewall-info.25/#post-6613
I've got dedicated server to run all my sites from.
I created domain and updated all DNS records to this server, everything is fine and propagated however when i try and receive mail nothing happens but it can send.
I went to dnsstuff.com and this is the error i got...
All connections to Mailservers port 25 have failed. The standard port
for SMTP transactions is 25, so your servers should be operating on
that port. It is recommended that it be fixed in order for your mail
service to operate properly. The Mail Servers that failed are:
xx.xxx.xxx.xxx | failed message send with: failed cx open with: failed socket connect with: Operation now in progress
/*****************
UPDATE
*****************/
Running a linux box using centOS.
The mailserver being used is, I believe, Postfix.
How do i fix this problem?
Check your firewall configuration on your server. If you can send from localhost (that is, direclty from your server), but mail can't be delivered from remote servers to your box, your firewall is the best bet to look at. Basically port 25 should be open to any IP. It's hard to give you specific details on how to configure your firewall, as you do not specify your OS and dikstribution. Most Linux distro's run some flavour of iptables. If iptables is what you have, you could try this command from the command line:
iptables -A INPUT -p tcp --dport 25 -j ACCEPT
Before you open up your firewall, you might want to dive into configuring postfix. It would not be nice to the rest of the world if you started running an open relay. That will get your server blacklisted in no time. This artice on the postfix website will give you a decent start.
I have chosen QuteCom SIP client for windows to chat.I have installed and configured the account with my public server. My SIP server is kamailio.The connection to the server is not established. The application is connecting to the server for a long time.
Any help is appreciated.
If looks like keep connecting, then I guess the SIP messages don't get to the server.
You can install Wireshark to monitor traffic on windows host on port 5060 (the SIP port) in order to see if SIP messages are sent to the server.
On server, you can install ngrep for the purpose of seeing if traffic from the phone comes there. The command would be like:
ngrep -d any -qt -W byline port 5060
If you don't see traffic coming to the SIP server, then might be a firewall or an ALG between the client and the server, or, a firewall even on client host or server itself.
If it is something in between (not on client host or server), then you should try to use TCP or better TLS.
Note that if you have the firewall on the server, you will see the SIP packets coming on the network, but they will be dropped by the kernel before getting to application layer. Typically on Linux you can see the firewall rules with:
iptables -L
If the SIP packets come to the server, then set debug=3 in kamailio.cfg, restart kamailio and watch the syslog file (e.g., /var/log/syslog or /var/log/messgaes) for kamailio-specific debug messages -- you should get hints of what happens during processing.
I have no trouble sending out email with my EC2 server, but how can I check the email that is sent to me? I have an elastic IP setup and modified reverse DNS records. Do I need to install Postfix to receive email?
Ensure that port 25 is active and open on your server. Install an SMTP service on your instance ...postfix is mighty fine.
Ensure you have also set up some MX records if you want to receive email from the world...
I suppose the first thing to do is testing if you can open a telnet connection to port 25 on your server. Then you know if anything is listening for incoming mail.
If not, then you should probably install postfix as well as test your firewall settings (I seem to recall the EC2 having some sort of firewall setting for which ports to allow in the web interface)
edit: correct port number