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[GH-ISSUE #867] SMTP Server Setup for receiving Pings #607

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opened 2026-02-25 23:43:00 +03:00 by kerem · 13 comments

kerem commented

2026-02-25 23:43:00 +03:00

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Originally created by @djarbz on GitHub (Jul 27, 2023).
Original GitHub issue: https://github.com/healthchecks/healthchecks/issues/867

I have been fighting with this all afternoon.
I have email notifications working, but I am unable to receive emails on my instance.

If I Telnet in, I can dump an email, but if I send an email from say my Gmail account, my instance will never receive it.
Actually, in Google Workspace, it will say rejected: The recipient server did not accept our requests to connect. Learn more at https://support.google.com/mail/answer/7720 [healthchecks.example.com. <REDACTED IP ADDRESS>: FAILED_PRECONDITION: connect error (111): Connection refused]

I know that my service is listening on port 25 and reachable externally, tested via telnet on a remote VPS as my ISP blocks port 25.

Originally created by @djarbz on GitHub (Jul 27, 2023). Original GitHub issue: https://github.com/healthchecks/healthchecks/issues/867 I have been fighting with this all afternoon. I have email notifications working, but I am unable to receive emails on my instance. If I Telnet in, I can dump an email, but if I send an email from say my Gmail account, my instance will never receive it. Actually, in Google Workspace, it will say rejected: `The recipient server did not accept our requests to connect. Learn more at https://support.google.com/mail/answer/7720 [healthchecks.example.com. <REDACTED IP ADDRESS>: FAILED_PRECONDITION: connect error (111): Connection refused]` I know that my service is listening on port 25 and reachable externally, tested via telnet on a remote VPS as my ISP blocks port 25.

kerem closed this issue

2026-02-25 23:43:00 +03:00

kerem commented

2026-02-25 23:43:01 +03:00

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@cuu508 commented on GitHub (Jul 31, 2023):

Can you test with a few other mail providers besides Gmail, to see if it's something Gmail-specific?

@cuu508 commented on GitHub (Jul 31, 2023): Can you test with a few other mail providers besides Gmail, to see if it's something Gmail-specific?

kerem commented

2026-02-25 23:43:01 +03:00

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@djarbz commented on GitHub (Jul 31, 2023):

Gmail is the only service that I have access to the server side logs to.
I did test with my work email and it bounced as well.

@djarbz commented on GitHub (Jul 31, 2023): Gmail is the only service that I have access to the server side logs to. I did test with my work email and it bounced as well.

kerem commented

2026-02-25 23:43:01 +03:00

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@cuu508 commented on GitHub (Jul 31, 2023):

Does sending test email from here work? https://sendtestemail.com/

@cuu508 commented on GitHub (Jul 31, 2023): Does sending test email from here work? https://sendtestemail.com/

kerem commented

2026-02-25 23:43:01 +03:00

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@djarbz commented on GitHub (Jul 31, 2023):

Unfortunately it did not work.

Date:
Jul 31 07:23:07

Email To:
8a6bf565-6ae0-4625-b54c-bca255df8654@<REDACTED>

Relay:
none

Connection Set-up Time:
0s

Send Time:
0s

Delivery Status Notification:
4.4.2

Status:
deferred

Email ID:
c07decfebaa4cee7e92b2437c192858d

This tool did work however: https://www.smtper.net/
I filled out the host/port/from/to fields.

@djarbz commented on GitHub (Jul 31, 2023): Unfortunately it did not work. ``` Date: Jul 31 07:23:07 Email To: 8a6bf565-6ae0-4625-b54c-bca255df8654@<REDACTED> Relay: none Connection Set-up Time: 0s Send Time: 0s Delivery Status Notification: 4.4.2 Status: deferred Email ID: c07decfebaa4cee7e92b2437c192858d ``` This tool did work however: https://www.smtper.net/ I filled out the host/port/from/to fields.

kerem commented

2026-02-25 23:43:01 +03:00

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@djarbz commented on GitHub (Jul 31, 2023):

In my registrar I do have the following records.
A - example.com --> server IP (ideally I would like this one to go away)
A - healthchecks.example.com --> server IP
MX - healthchecks.example.com --> healthchecks.example.com priority 10

@djarbz commented on GitHub (Jul 31, 2023): In my registrar I do have the following records. A - example.com --> server IP (ideally I would like this one to go away) A - healthchecks.example.com --> server IP MX - healthchecks.example.com --> healthchecks.example.com priority 10

kerem commented

2026-02-25 23:43:01 +03:00

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@cuu508 commented on GitHub (Jul 31, 2023):

In https://www.smtper.net/ the default port is 25 – did you leave it as-is, or did you specify a different port?

@cuu508 commented on GitHub (Jul 31, 2023): In https://www.smtper.net/ the default port is 25 – did you leave it as-is, or did you specify a different port?

kerem commented

2026-02-25 23:43:01 +03:00

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@djarbz commented on GitHub (Jul 31, 2023):

I did use port 25.

@djarbz commented on GitHub (Jul 31, 2023): I did use port 25.

kerem commented

2026-02-25 23:43:01 +03:00

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@cuu508 commented on GitHub (Jul 31, 2023):

I'm not sure what to make of it – perhaps the server running your Healthchecks instance has port 25 blocked to/from some destinations but not all?

@cuu508 commented on GitHub (Jul 31, 2023): I'm not sure what to make of it – perhaps the server running your Healthchecks instance has port 25 blocked to/from some destinations but not all?

kerem commented

2026-02-25 23:43:01 +03:00

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@djarbz commented on GitHub (Jul 31, 2023):

This is really weird, I just got a bunch of emails to come through on my test check.

Thing is, I didn't change anything...

@djarbz commented on GitHub (Jul 31, 2023): This is really weird, I just got a bunch of emails to come through on my test check. Thing is, I didn't change anything...

kerem commented

2026-02-25 23:43:01 +03:00

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@cuu508 commented on GitHub (Jul 31, 2023):

Another guess – perhaps it's something to do with DNS caching?

Say, if you were changing the A and MX records for healthchecks.example.org, perhaps the old values were still in some DNS resolver caches. Once the cached values expired, the deferred emails could come through?

@cuu508 commented on GitHub (Jul 31, 2023): Another guess – perhaps it's something to do with DNS caching? Say, if you were changing the A and MX records for healthchecks.example.org, perhaps the old values were still in some DNS resolver caches. Once the cached values expired, the deferred emails could come through?

kerem commented

2026-02-25 23:43:01 +03:00

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@djarbz commented on GitHub (Jul 31, 2023):

I haven't touched them since Friday.

@djarbz commented on GitHub (Jul 31, 2023): I haven't touched them since Friday.

kerem commented

2026-02-25 23:43:01 +03:00

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@cuu508 commented on GitHub (Jul 31, 2023):

Well then maybe that's not it (assuming short TTLs before the changes).

In any case, it's not yet clear to me there's anything to fix for me here. If you manage to isolate the problem to something in the Healthchecks codebase, I'm all ears.

@cuu508 commented on GitHub (Jul 31, 2023): Well then maybe that's not it (assuming short TTLs before the changes). In any case, it's not yet clear to me there's anything to fix for me here. If you manage to isolate the problem to something in the Healthchecks codebase, I'm all ears.

kerem commented

2026-02-25 23:43:01 +03:00

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@djarbz commented on GitHub (Jul 31, 2023):

Yeah, I think I can close this out. I just wish I knew what the issue was.

@djarbz commented on GitHub (Jul 31, 2023): Yeah, I think I can close this out. I just wish I knew what the issue was.