NAS540 - Troubleshooting email settings

MV10 · July 2020

As far as I can tell, the NAS540 can only send email to the unencrypted SMTP port 25 (which is ridiculous). Because of this, I set up E-Mail Relay on a Raspberry Pi to forward to GMail's TLS SMTP. I know it works, I did a quick telnet test from my Windows desktop. I don't currently have it configured to require credentials which means the NAS configuration ought to be dead easy:

To: me@gmail.com
From: backup-NAS@foo.com
Server: raspberrypi.local

But all I get is that terse, useless, "Error" message. Is there a log somewhere, maybe something I can ssh into and tail follow?

#NAS_July_2020

MV10 · July 2020

For what it's worth, I can telnet from the NAS to the mail relay over ssh so it isn't basic connectivity -- which I knew since the Pi writes to the NAS itself, but I wasn't having ideas about anything else to try.

Mijzelf · July 2020

You can run tcpdump on the Pi, or something like that, to read the SMTP conversation.

MV10 · July 2020

Running this on the Pi shows nothing, which suggests the NAS isn't even trying to connect (that IP is the NAS).

sudo tcpdump -i any -nn src 192.168.1.200 and port 25

Pretty sure that command is ok, if I ssh to the NAS and telnet to port 25, the Pi does respond with the 220 Email Relay message, and tcpdump does show traffic in the Pi terminal:

07:23:32.037167 IP 192.168.1.200.35326 > 192.168.1.16.25: Flags [S], seq 418944381, win 14600, options [mss 1460,nop,nop,TS val 68997187 ecr 0,nop,wscale 5], length 0<br>07:23:32.039579 IP 192.168.1.200.35326 > 192.168.1.16.25: Flags [.], ack 1790121067, win 457, options [nop,nop,TS val 68997196 ecr 1190322094], length 0<br>07:23:32.045267 IP 192.168.1.200.35326 > 192.168.1.16.25: Flags [.], ack 56, win 457, options [nop,nop,TS val 68997197 ecr 1190322097], length 0<br><br>

(Wow, this forum software is truly awful ... the above only shows part of what I pasted into the editor -- but you get the idea.)

The NAS accepts "raspberrypi.local" as the SMTP server, but I think those are served by mDNS (multicast) and not regular DNS (router/public), so maybe name resolution fails? (It's absurd that it won't just accept an IP address... who writes this stuff???)

I kind of wonder about monitoring traffic on the NAS itself. I don't know anything about BusyBox, can tcpdump be installed on the NAS? Is that a Really Bad Idea for some reason? My NAS doesn't do anything but run the single-volume RAID5 array, I don't have other optional apps installed or running except rsync backups, so space isn't an issue.

I did try "install tcpdump" but apparently it's more complicated than that (I've been spoiled by apt-get).

MV10 · July 2020

Realized I can tcpdump the mDNS port (5353) on the Pi and it does seem that the NAS tries to resolve "raspberrypi.local" when I hit the apply button to send the test email.

Mijzelf · July 2020

You can add raspberrypi.local to /etc/hosts, to test if it's a dns issue. Unfortunately that is not a direct solution, as it's a volatile file.

And no, it's not a 'bad idea' to install tcpdump. But 'install tcpdump' indeed won't work. The only available package manager is the one in the webinterface, although I think it has a commandline interface either.

But you can install Entware-ng, which has a big repository. You could install an smtp relay on the nas itself (and look in /etc/hosts which hostname can be used)

MV10 · July 2020

Thanks for the ideas. I'm trying to understand the scope of change that installing Entware implies (I'm an experienced developer, ~40 years, but have only been playing with Linux for a couple months). It looks pretty interesting, the same email relay I already added to the Pi is even there.

Would it replace BusyBox? No impact to the GUI? (I only care about the RAID / Volume management and maintenance -- not ready to go console-commando for that stuff yet.)

Thinking the NAS542 instructions are probably close enough:

https://github.com/Entware/Entware/wiki/Install-on-Zyxel-NAS542

MV10 · July 2020

Oh, I see, it's just a package manager. Very cool. I'll give it a shot.

MV10 · July 2020

Hmm... those instructions leave a bit to be desired (er... learning opportunity).

I had a thought while working on installation -- will a firmware update wipe all of this out? (I'm vaguely aware this can be set up on a USB drive, are there instructions somewhere?)

Edit: I'm stuck at step 5 of the Entware instructions linked earlier at step 5 -- modifying the path automatically at startup. On desktop Linux I understand how to do this, but I'm not sure what folders are "real" (will survive reboot) on the NAS. I'd appreciate some tips/advice. (I'd need to ask this eventually to set up the email relay!)

On the plus side, once I get it working I'll go ahead and update those ZyXel install instructions with corrections and details to help the next guy.

Mijzelf · July 2020

There is an easier way, you can use the firmware package manager, after you install MetaRepository. (Scroll down for instructions)

MV10 · July 2020

Thanks, installing your meta repo is easy, but I don't understand what that simplifies for me regarding Entware. (I am installing it anyway though, it has nano, and vi gives me a headache!)

NAS540 - Troubleshooting email settings

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