Debugging Reacher

How to check if port 25 is open?

When choosing a server to install Reacher on, you need to make sure that the server itself has port 25 open AND the chosen cloud provider allows outbound port 25 connections on its network.

To test this, there are two methods:

  1. curl (try this first)

  2. telnet (more advanced)

1. Test port 25 with curl

Paste the following command in the shell of your server.

curl -sSf --verbose -k smtp://alt1.gmail-smtp-in.l.google.com:25 --ssl-reqd --mail-from test@gmail.com --mail-rcpt test@gmail.com
✅ Here's the expected output when port 25 works:
* About to connect() to alt1.gmail-smtp-in.l.google.com port 25 (#0)
*   Trying 142.250.153.26...
* Connected to alt1.gmail-smtp-in.l.google.com (142.250.153.26) port 25 (#0)
< 220 mx.google.com ESMTP he11-20020a1709073d8b00b006e862100d5bsi2937572ejc.396 - gsmtp
> EHLO reacher
< 250-mx.google.com at your service, [176.31.197.159]
< 250-SIZE 157286400
< 250-8BITMIME
< 250-STARTTLS
< 250-ENHANCEDSTATUSCODES
< 250-PIPELINING
< 250-CHUNKING
< 250 SMTPUTF8
> STARTTLS
< 220 2.0.0 Ready to start TLS
* Initializing NSS with certpath: sql:/etc/pki/nssdb
* skipping SSL peer certificate verification
* SSL connection using TLS_ECDHE_ECDSA_WITH_AES_128_GCM_SHA256
* Server certificate:
* 	subject: CN=mx.google.com
* 	start date: May 04 17:12:30 2022 GMT
* 	expire date: Jul 27 17:12:29 2022 GMT
* 	common name: mx.google.com
* 	issuer: CN=GTS CA 1C3,O=Google Trust Services LLC,C=US
> EHLO reacher
< 250-mx.google.com at your service, [176.31.197.159]
< 250-SIZE 157286400
< 250-8BITMIME
< 250-ENHANCEDSTATUSCODES
< 250-PIPELINING
< 250-CHUNKING
< 250 SMTPUTF8
> MAIL FROM:<test@gmail.com>
< 250 2.1.0 OK he11-20020a1709073d8b00b006e862100d5bsi2937572ejc.396 - gsmtp
> RCPT TO:<test@gmail.c>
< 550-5.1.1 The email account that you tried to reach does not exist. Please try
< 550-5.1.1 double-checking the recipient's email address for typos or
< 550-5.1.1 unnecessary spaces. Learn more at
< 550 5.1.1  https://support.google.com/mail/?p=NoSuchUser he11-20020a1709073d8b00b006e862100d5bsi2937572ejc.396 - gsmtp
* RCPT failed: 550
> QUIT
< 221 2.0.0 closing connection he11-20020a1709073d8b00b006e862100d5bsi2937572ejc.396 - gsmtp
* Closing connection 0
curl: (55) RCPT failed: 55

2. Test port 25 with telnet

Paste the following command in the shell of your server.

telnet alt1.gmail-smtp-in.l.google.com 25
✅ Click to see expected output when port 25 is open:
# This means that connection to port 25 on Google's server is established.
Trying 142.250.153.26...
Connected to alt1.gmail-smtp-in.l.google.com.
Escape character is '^]'.
220 mx.google.com ESMTP t2-20020a056402524200b0041d70e3a2b0si10608932edd.55 - gsmtp
# You can type 'QUIT' to quit this prompt
❌ Click to see unsuccessful output:
Trying 142.250.153.26...
# This step can hang for a couple of seconds...
telnet: Unable to connect to remote host: Connection refused

Which cloud providers have port 25 open?

Here are details about some of the most well-known providers:

  • ⚠️ AWS: Needs an application to open port 25, link to apply (Dec 2020).

  • ⚠️ Digital Ocean: Your account needs to be 60d old, then you can apply to open port 25 (Mar 2020).

  • ❌ GCP: Port 25 closed, source.

  • ❌ Heroku: Starting from July 2021, Heroku blocks port 25 intermittently according to this document.

  • ⚠️ Hetzner: Port 25 open according to unofficial source (Feb 2021), but seems now that you need to request manually.

  • ⚠️ Linode: Port 25 closed for new accounts, but can be opened if reverse DNS is set up correctly, source (Apr 2022).

  • ✅ OVH: Port 25 open on new instances, but outbound port 25 traffic is monitored to prevent spam (May 2022).

  • ⚠️ Vultr: Create support ticket to open port 25, source, though recent reports (May 2022) show that they won’t do it anymore.

How can I debug "is_reachable": "unknown"?

In most cases, if you have a TimeoutError, it means that port 25 is closed. Refer to the questions above about opening port 25.

In other cases, you can enable the RUST_LOG=debug environment variable on your server or on your Docker container. Then, by looking at the logs when performing an email verification, you can debug why is_reachable is unknown. Some example of logs you might find:

  • IP Blacklisted:

    5.7.1 Service unavailable; Client host [<YOUR_IP>] is blacklisted. Visit https://www.sophos.com/en-us/threat-center/ip-lookup.aspx?ip=<YOUR_IP> to request delisting

  • Your FROM field does not match the reverse DNE (mxgmx117) Nemesis ESMTP Service not available; No SMTP service;

For assistance in debugging these errors, please contact amaury.

Contact me

If you encounter any issue that you don't know how to solve, simply send me an email to amaury.

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