Inbound email issue

[oldboy47]

Afternoon, but not good. Yesterday my internet service ground almost to a halt. My ISP suggested that my ADSL modem, directly connected to a network card on my server (SBS 2003) was probably the cause. Up until then email in and out working fine. Replaced the old modem (it was really old) with a Netgear DM200 and got that working. Browsing the internet at unheard of speeds in excess of 1mb (we are pretty rural in a now built up area). Mail flies out but heres the problem - it will not come in. I can do web based mail in and out (Hotmail) but cannot get mail in to the server. Have set port forwarding for SMTP to port 25 on the DM200, nothing has been changed on the server. ISP have helped as much as they can and Netgear have said the settings are OK on the modem.
Would appreciate any advice please.

[peterb]

Port 25 is the outgoing mail port and if mail is going out OK.

The incoming mail port depends on the protocol, POP is normally 110, secure POP is usually 995; 143 and 993 are used for standard and secure IMAP.

But these are all pull protocols so the router should be allowing in packets from those requests. Does going back to the old router fix the problem?

You could try opening up incoming connections on the appropriate port (just as a test) but I suspect the problem is actually with your computer settings, however going back to the old router will confirm whether that is the case or not.

[oldboy47]

Thanks for the reply Peter. Yes I did think that connecting back the old modem my resolve the problem temporarily but unfortunately it didn't. I had considered that it might be something on the server but I have made no changes to that from before the speed problem.
Is your suggestion that I open up ports 110,143,993 and 995 on the DM200 ? Are there any others that could be available/useful - I'd just like to collect my inbound mail.

[peterb]

If the problem persists with the old router, it isn't a router problem! Opening up the ports shouldn't be necessary as the client requests the mail which will open the port for the reply.

I would check the settings on the mail client in the first instance.

[Splash]

Put your mailserver DNS address into the checker at https://mxtoolbox.com/diagnostic.aspx - this runs a bunch of tests against it and should give you some indication as to where your issue lies.

At a guess though: your SBS box is configured for SMTP inbound mail delivery (rather than to pick up email from a mailbox at your ISP using POP3 or IMAP), and your firewall rules on your DM200.

That said: is your DM200 configured as a router or a modem? If the latter then routing is done on your SBS server (in ISA, if you have SBS Advanced). If it's being used as a router... has your SBS server got a static IP address, or is it DHCP? If DHCP then your ip address may change, breaking your port forwarding for TCP25 inbound (and stopping SMTP delivery from working)

[oldboy47]

Thanks Peter and Splash. The SBS has a static IP address - The router has the first address and a second card in the SBS has the second address. Separately the SBS provides DHCP to the internal network.

[DanceswithUnix]

Back to basics.

Use telnet (or putty in Windows land) to try and connect to port 25 of your server's local IP address on the LAN. Here's me connecting to my home server from a Linux command line and then just issuing the "quit" command (some bits changed so you don't all know my email address!)

$ telnet gate 25
Trying 192.168.100.1...
Connected to gate.
Escape character is '^]'.
220 example.com ESMTP Exim 4.90_1 Tue, 29 May 2018 13:02:27 +0100
quit
221 example.com closing connection
Connection closed by foreign host.
$

If that works then your server is OK so you need to find a connection outside the house and see if the port is forwarding OK.

My last problem like that, there was a tick box marked "enable" in the router forwarding rule which I hadn't ticked. It will likely be something as stupid as that

[oldboy47]

Thanks again guys. Already had a friend attempt telnet to port 25 and got the message - could not open connection to host on port 25, connect failed. He also tried without stipulating a port but that failed too.

[Dashers]

Back up a bit. Could you clarify, are you hosting your own SMTP server and mailboxes on your SBS box?

If not, where are you connecting out to to get your mail?

If you are hosting your own mail, then mail should be delivered via SMTP over port 25. Tap the domain name that your server is the MX for into mxtoolbox.com (or similar) to get a detailed report of whether it can contact the SMTP server.

If remote servers cannot connect to port 25, then you need to look at how your connection is meant to be setup. Most "home" users will use a port-forward to direct a single port (e.g. 25) through to an internal IP address. But you might be using a 1:1 NAT or a bridged connection with a routable IP address on your SBS.

Are you able to verify that your external IP address(es) haven't changed? e.g., Google "what's my ip" and is it different to what it was before?

[DanceswithUnix]

Thanks again guys. Already had a friend attempt telnet to port 25 and got the message - could not open connection to host on port 25, connect failed. He also tried without stipulating a port but that failed too.

I was rather expecting that, but the main point was if you are connected on the same switch as the server sat right next to the server can you telnet to it using the *internal* IP address.

Above telnet connected to 192.168.100.1, that isn't my public IP address. The router then has to port forward to the internal address, but if the email server isn't talking locally then all bets are off.

Not stipulating a port should always fail, telnet is a laughably insecure service which should never be enabled on anything under any circumstances, but the telnet client is dead handy for debugging problems with web, email and ftp servers.