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Deferred: 421 Too many concurrent SMTP connections;

PostPosted: Thu Sep 29, 2011 6:02 pm
by gourmet
Subject says it all. That's what SG is replying to SMTP sessions.

After thinking a while I just made this SMTP status check service.

If you find out that email isn't being forwarded normally through SG you can check this url to see SMTP servers status.

http://s.sami-lehtinen.net/c/sc?sg

Re: Deferred: 421 Too many concurrent SMTP connections;

PostPosted: Tue Mar 10, 2020 8:15 pm
by lwc
The aforementioned URL is dead, any chance you'll bring it back to life?

In any case, lately my hosting can no longer write me any messages!
They told me they simply get "Too many concurrent SMTP connections from this IP address; please try again later."
Their IP is 198.61.254.17 and they welcome you to white list if that's the only way.

Below is their log, what could be done? Thanks in advance!

Code: Select all
"delivery-status": {
"mx-host": "gourmet7.spamgourmet.com",
"code": 421,
"description": "",
"session-seconds": 2.9281630516052246,
"retry-seconds": 14400,
"attempt-no": 7,
"message": "Too many concurrent SMTP connections from this IP address; please try again later."
},
"recipient-domain": "neverbox.com",
"event": "failed",
"campaigns": [],
"reason": "generic",
"user-variables": {},
"flags": {
"is-routed": false,
"is-authenticated": true,
"is-system-test": false,
"is-test-mode": false
},
"log-level": "warn",
"timestamp": 1583648629.919381,
"envelope": {
"transport": "smtp",
"sender": "no-reply@fastcomet.com",
"sending-ip": "198.61.254.17",
"targets": "[censored]@neverbox.com"
},
"message": {
"headers": {
"to": "Name <[censored]@neverbox.com>",
"message-id": "c62aa3c5dc911ec03cd2d1ca651a0c09@my.fastcomet.com",
"from": "FastComet General Support <no-reply@fastcomet.com>",
"subject": "[Ticket ID: 256612] [censored]"
},
"attachments": [],
"size": 2769
},
"recipient": "[censored]@neverbox.com",

Re: Deferred: 421 Too many concurrent SMTP connections;

PostPosted: Wed Mar 11, 2020 5:33 am
by gourmet
The server mentioned earlier is currently running in environment where connectivity is really limited on purpose. As example no SMTP connections are allowed.

But there are many other similar or even lot better and versatile tools and SMTP testing services, like the MXtoolbox which is actually quite handy in many situations.

But based on the error message from this IP address, it would indicate it's IP address specific error, and not a global error.

Re: Deferred: 421 Too many concurrent SMTP connections;

PostPosted: Sat Jun 20, 2020 11:21 pm
by isbbs.thebluecat
Hi Lwc and Gourmet,

Please, also see related issue https://bbs.spamgourmet.com/viewtopic.php?f=4&t=1819&sid=3e75f041ff053e35d21a93668dcb6c4c

We are also still waiting for a SpamGourmet Admin to give us some support. :)

Best regards,

A really happy customer of SpamGourmet

Re: Deferred: 421 Too many concurrent SMTP connections;

PostPosted: Wed Jul 15, 2020 6:36 pm
by score
I currently have this issue specifically with Patreon's login service (though not their customer support). I don't know if it affects other mail providers.

Attached is part of the exchange with their support team:

Our support emails send via Zendesk, which is different from our Patreon.com emails which send from specific emails and IP addresses. I've found that private domain email service providers sometimes don't play well with our email notifications.

I looked into our email sending logs, and it looks like recently our emails are failing to reach your inbox. When we attempt to deliver your emails, we receive this response: Too many concurrent SMTP connections from this IP address; please try again later.

It's possible that your email provider is marking Patreon emails as spam, or blocking them from hitting your inbox. Whitelisting Patreon's email will allow all emails to be successfully delivered to your inbox.

When requesting to whitelist Patreon's emails, it's good to know that we primarily send emails through bingo@patreon.com and no-reply@patreon.com. The IP addresses our emails come from are:


159.135.225.154

159.135.225.155

159.135.225.156

69.72.32.187

166.78.71.13

166.78.71.14

Re: Deferred: 421 Too many concurrent SMTP connections;

PostPosted: Sun Nov 29, 2020 2:14 pm
by jolinwarren
score wrote:I currently have this issue specifically with Patreon's login service (though not their customer support).


I am having the exact same problem, and their support gave me the same error message ("Too many concurrent SMTP connections from this IP address"). Did you ever resolve this issue?

Re: Deferred: 421 Too many concurrent SMTP connections;

PostPosted: Sun Nov 29, 2020 9:45 pm
by score
jolinwarren wrote:
score wrote:I currently have this issue specifically with Patreon's login service (though not their customer support).


I am having the exact same problem, and their support gave me the same error message ("Too many concurrent SMTP connections from this IP address"). Did you ever resolve this issue?


I never really resolved it in a satisfactory way that allowed me to continue using spamgourmet, but I did (after a 3-month support ticket) get them to change the email address associated with my account to a different one.

Re: Deferred: 421 Too many concurrent SMTP connections;

PostPosted: Thu Feb 04, 2021 8:33 pm
by jj05
This affects everything that uses MailGun, e.g. Kraken, Patreon, etc. There are a couple of threads open already, but it doesn't look any solution is forthcoming.

Re: Deferred: 421 Too many concurrent SMTP connections;

PostPosted: Fri Jan 14, 2022 6:07 pm
by gregp01
I'm seeing the same problem - I've been unable to receive certain emails from BackerKit (a helper service for Kickstarter and other crowdfunding sites) for a while now. I finally was able to contact a support person on their end, and apparently the SpamGourmet servers are refusing connections from their vendor's email server, with the same message: "Too many concurrent SMTP connections from this IP address; please try again later."

Is there any way to diagnose this further on the SpamGourmet end? For example, could it be that their server is keeping connections open too long, and/or opening too many connections at once to send emails to many SG users at the same time?

BackerKit uses MailGun, so this may be a configuration issue with MailGun, but since none of us are MailGun customers I don't see how we can get their attention.

Perhaps SpamGourmet could whitelist MailGun's IPs, and/or increase the limit on concurrent conections?

Re: Deferred: 421 Too many concurrent SMTP connections;

PostPosted: Thu Jan 27, 2022 2:55 pm
by ddddddd
Hi there - getting the same problem with Patreon. Anyone got any news or potential solution?

Re: Deferred: 421 Too many concurrent SMTP connections;

PostPosted: Sat Jan 29, 2022 12:51 pm
by jolinwarren
Unfortunately, I think the only solution is to not use a SpamGourmet address :(

Re: Deferred: 421 Too many concurrent SMTP connections;

PostPosted: Wed Feb 02, 2022 3:15 pm
by gregp01
I heard back again from BackerKit, but it seems that they are not able to make any changes on their end which would fix this problem, as they don't have that level of control over how MailGun sends emails. Supposedly they contacted MailGun about this, but they have not heard back.

If the people who are paying MailGun can't even get a response from them about this issue, let alone a solution, then I suspect there is no hope for getting it fixed on the sending end.

Is there nothing that can be done on the Spam Gourmet end to get this working? If we could get a list of IPs or domains used by MailGun, they could potentially be added to an allow list with a bigger concurrent connection limit.

BackerKit was able to update my email address in their system to a Gmail one, which solves my problem of not getting their emails, but of course means that I can't use SG protection on anything with them in the future, and it's not like I get to choose which Kickstarter or other crowdfunding campaigns use BackerKit.

Re: Deferred: 421 Too many concurrent SMTP connections;

PostPosted: Mon Aug 29, 2022 10:42 am
by mux951
there seems to have been some changes eigther by Spamgourmet or Backerkit because I have started receiving emails again.

Background: I also got the delivery issues with Backerkit. I got in contact with Backerkit Support and found the same results/ issues as mentioned before (Patreon, etc.). Didn't mention it because the issue was already known.
According to my documentation this issue started sometime after 02.August.2019 (last email received) and now ended sometime before 19.July.2022 (first email received).

Can somebody confirm this has been resolved with Patreon, etc. (I don't have an account there)?
Maybe this information also helps the development team if there have been any changes recently.

Re: Deferred: 421 Too many concurrent SMTP connections;

PostPosted: Thu May 04, 2023 8:33 pm
by Fosaf
bouncing this topic as mailgun failed to get an email to me and I highly suspect it's this issue.

Re: Deferred: 421 Too many concurrent SMTP connections;

PostPosted: Fri May 05, 2023 10:52 am
by Fosaf
As seen in this screenshot, MailGun even does exponential backoff. Still they must be doing something weird, maybe not closing the TCP connections?
(I got the screenshot from the owner of the site whose email didn't reach me.)