Connection reset by peer (os error 104)

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1

I’m currently having issues trying to reach Vodafone Deutschland. Telnetting to the IP address seems to work fine without any issues. Any ideas what could be wrong?

KumoMTA internal: failed to connect to any candidate hosts: connect to ResolvedAddress { name: \"mx5.vodafonemail.de.\", addr: 2.207.151.53 } port 25 and read initial banner: reading banner: IO error: Connection reset by peer (os error 104): Connection reset by peer (os error 104)

root@mta3:~# telnet 2.207.151.53 25
Trying 2.207.151.53...
Connected to 2.207.151.53.
Escape character is '^]'.
220 mx5.vodafonemail.de ESMTP MX
EHLO test
250-mx5.vodafonemail.de
250-PIPELINING
250-SIZE 45000000
250-ETRN
250-STARTTLS
250-ENHANCEDSTATUSCODES
250-8BITMIME
250 CHUNKING
HELP
500 5.5.2 Error: command not recognized
QUIT
221 2.0.0 Bye
Connection closed by foreign host.
3

No issues connecting with OpenSSL either.

4

I know a TCP reset or drop is normal, but this issue has been persistent for days now

5

Just with this address, for some reason

6

You will want to do an outbound trace in kcli.

7

Thank you so much!

8

Welp

9 
[f8208d32-0e93-4e4a-9e82-6ba46cc0abfd]       === BeginSession 2025-01-24 00:12:23.420540667 UTC
[f8208d32-0e93-4e4a-9e82-6ba46cc0abfd]       === conn_meta egress_pool="pool-11"
[f8208d32-0e93-4e4a-9e82-6ba46cc0abfd]       === conn_meta egress_source="ip-11"
[f8208d32-0e93-4e4a-9e82-6ba46cc0abfd]       === conn_meta id="f8208d32-0e93-4e4a-9e82-6ba46cc0abfd"
[f8208d32-0e93-4e4a-9e82-6ba46cc0abfd]       === conn_meta mx_plan={"Addresses":[{"addr":"2.207.151.53","name":"mx5.vodafonemail.de."}]}
[f8208d32-0e93-4e4a-9e82-6ba46cc0abfd]       === conn_meta ready_queue_name="ip-11->mx5.vodafonemail.de@smtp_client"
[f8208d32-0e93-4e4a-9e82-6ba46cc0abfd]  78µs === INFO: Attempting connection to ResolvedAddress { name: "mx5.vodafonemail.de.", addr: 2.207.151.53 } port 25
[f8208d32-0e93-4e4a-9e82-6ba46cc0abfd]   3ms === Connected
[f8208d32-0e93-4e4a-9e82-6ba46cc0abfd]   3ms === conn_meta mx_address="2.207.151.53"
[f8208d32-0e93-4e4a-9e82-6ba46cc0abfd]   3ms === conn_meta mx_host="mx5.vodafonemail.de."
[f8208d32-0e93-4e4a-9e82-6ba46cc0abfd]   3ms === conn_meta source_address="X.X.X.X:51923"
[f8208d32-0e93-4e4a-9e82-6ba46cc0abfd]   5ms === Closed
[f8208d32-0e93-4e4a-9e82-6ba46cc0abfd]       === ERROR: connect to ResolvedAddress { name: "mx5.vodafonemail.de.", addr: 2.207.151.53 } port 25 and read initial banner: reading banner: IO error: Connection reset by peer (os error 104): Connection reset by peer (os error 104)
[f8208d32-0e93-4e4a-9e82-6ba46cc0abfd]       === conn_meta egress_pool="pool-11"
[f8208d32-0e93-4e4a-9e82-6ba46cc0abfd]       === conn_meta egress_source="ip-11"
[f8208d32-0e93-4e4a-9e82-6ba46cc0abfd]       === conn_meta id="f8208d32-0e93-4e4a-9e82-6ba46cc0abfd"
[f8208d32-0e93-4e4a-9e82-6ba46cc0abfd]       === conn_meta mx_address="2.207.151.53"
[f8208d32-0e93-4e4a-9e82-6ba46cc0abfd]       === conn_meta mx_host="mx5.vodafonemail.de."
[f8208d32-0e93-4e4a-9e82-6ba46cc0abfd]       === conn_meta mx_plan={"Addresses":[{"addr":"2.207.151.53","name":"mx5.vodafonemail.de."}]}
[f8208d32-0e93-4e4a-9e82-6ba46cc0abfd]       === conn_meta ready_queue_name="ip-11->mx5.vodafonemail.de@smtp_client"
[f8208d32-0e93-4e4a-9e82-6ba46cc0abfd]       === conn_meta source_address="X.X.X.X:51923"
10

It seems to connect and then suddenlyy the connection drops a few milliseconds later. Huh

11

Is this one the one IP or all of them?

12

All of them

13

Ooh, let me try a different IP range

14

Maybe, Vodafone doesn’t like one of my ranges for some reason

15

And all MXes or that one?

16

They only have one MX record, ha

17

And just the one host?

18

Yep

19

I’d try another range, if it works then codaphone doesn’t like the current one.

20

It worked!

21

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