Unable to setup a functional SMTP account with local cloudron mailbox

[overclockmp]

Hello everyone,

I am currently trying to setup a send email node in n8n.
I have done what was suggested here and I created a specific user for this. I have also setup a mailbox associated to that user.

Outbound emails work fine already with any apps (relay through mailjet).
I have added the new user email as a sender in mailjet config.

I have used the credentials from that new user to setup the n8n SMTP account.
I use port 587 and mail.<domain> as the host.
SSL is disabled and STARTTLS is enabled.

I have also added the client host name as the n8n hostname.

Is there a better way to do this now? (this linked post is from 2021, so maybe this information is outdated).
Is there something I missed?

Thank you all for your help

[joseph]

@overclockmp I would say first test using swaks. Open a web terminal and use swaks to test your credentials. Something like:

swaks --server my.domain.com -p 587 --from "from@domain.com" --body "Test mail" --auth-user "from@domain.com" --auth-password "password"

[overclockmp]

Hi @joseph, thanks for the assistance.
Running the command above with --server mail.domain.com, I get "Network Unreachable".
Running it with --server my.domain.com, I get "Connection Timeout".
Under Email > Domain > Status, the outbound SMTP is green.

The more I look into this, the more it seems that I would have to use mailjet directly instead of going through the outbound SMTP, but I am not sure if it's a good approach.

[overclockmp]

Hello , just following up here to see if there are any other ideas...
Thanks for the help

[james]

Hello @overclockmp
Could you please share a screenshot of your N8N configuration for SMTP?

[joseph]

@overclockmp said in Unable to setup a functional SMTP account with local cloudron mailbox:

Running the command above with --server mail.domain.com, I get "Network Unreachable".
Running it with --server my.domain.com, I get "Connection Timeout".

I would start here... Can you ping/host/dig mail.domain.com ? Can you telnet mail.domain.com 587 ?

[overclockmp]

Apologies for the delay, I must have missed the notification with the holidays. Thanks for your answer.

@joseph,

Can you ping/host/dig mail.domain.com?

Yes, using dig from n8n web terminal:

# dig mail.domain.com
; <<>> DiG 9.18.30-0ubuntu0.24.04.2-Ubuntu <<>> mail.domain.com
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 27695
;; flags: qr rd ra; QUERY: 1, ANSWER: 2, AUTHORITY: 0, ADDITIONAL: 1

;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 65494
;; QUESTION SECTION:
;mail.domain.com.               IN      A

;; ANSWER SECTION:
mail.domain.com.        0       IN      CNAME   my.domain.com.
my.domain.com.  0       IN      A       192.168.1.3

;; Query time: 44 msec
;; SERVER: 127.0.0.11#53(127.0.0.11) (UDP)
;; WHEN: Sat Dec 27 16:19:45 UTC 2025
;; MSG SIZE  rcvd: 81

Using host from n8n web terminal:

# host mail.domain.com
mail.domain.com is an alias for my.domain.com.
my.domain.com has address 192.168.1.3
my.domain.com has IPv6 address 2606:4700:130:436c:6f75:6466:6c61:7265

Can you telnet mail.domain.com 587?

No, it hangs and times out on the web terminal and connection is refused through ssh:

# telnet mail.domain.com 587
Trying 192.168.1.3...
Connection failed: Connection timed out
Trying 2606:4700:130:436c:6f75:6466:6c61:7265...
telnet: Unable to connect to remote host: Network is unreachable

It is probably worth noting that I am using a pihole as local DNS. Not sure if it has any impact...

[overclockmp]

Hi @james, here is a redacted screenshot that should match my description at the beginning of this thread:

[joseph]

@overclockmp so the problem is that connection to port 587 is not working. This is not a DNS problem (from what I can tell). You can try telnet 192.168.1.3 587 . This is not working and it's some networking issue in your set up. Maybe the VM/hypervisor settings should allow port 587 to be looped back?

[overclockmp]

Thank you. I shall investigate the host OS iptables config then.
The thing that I fail to understand is that other apps seem to be able to send emails without any issues, through that mailjet relay. So I don't quite understand what's different here with this current configuration in n8n. My apologies if I am missing something very trivial here...

[overclockmp]

Ok, so after looking into open ports a bit more, it turns out that there is nothing listening on port 587. As such, there is no SMTP server running or listening to any port whatsoever. I figure that an SMTP server may only start running if I enable incoming emails (setting which was not enabled, purposefully). When I enabled incoming email setting, sudo netstat -tlnp | grep 587 was finally returning something and n8n configuration worked fine.

So to sum up, if my understanding is correct, when only using outbound mail, there isn't an actual SMTP server running, but only some kind of abstraction that containerized apps can use to send email directly through the mail relay (the internals of this are fuzzy to me...), so I need to enable incoming emails in order to send emails...

But I'm glad I was at least able to make this work before going into 2026. Thanks for the help and for putting me on the right path here.

Thank you for all the great work you do Cloudron Team, and wishing you all the best for the new year :).