#5.5.1 RCPT first

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1

Hi teams

I find a problem. Currently, it only appears in one customer email (xxx@f5.com)

At first I didn’t think it was a problem with KUMOMTA, I sent other email addresses without any problem.
This email address(xxx@f5.com) has been retryed 30 times and it still failed.

one more question is : error:503 needs to continue to try again, should it be considered an error?

The error message is:

[
    {
        "type": "TransientFailure",
        "tls_cipher": "TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384",
        "size": 13491,
        "bounce_classification": "Uncategorized",
        "peer_address": {
            "addr": "139.138.xx.xx",
            "name": "mx1.hc5801-97.iphmx.com."
        },
        "egress_source": "xxx",
        "tls_protocol_version": "TLSv1_2",
        "sender": "marketing@xx.xxx.com",
        "egress_pool": "xxxxx",
        "delivery_protocol": "ESMTP",
        "headers": {},
        "timestamp": 1748428119,
        "meta": {
            "Subject": "Welcome to join us ~"
        },
        "queue": "xxxx@f5.com",
        "nodeid": "77a6fd6d-470e-4456-83c3-68aa67c681ea",
        "id": "83ff345b3bae11f088a4bc241199e9bd",
        "session_id": "3c9c8510-0ef7-49b4-b438-3ad299683d0e",
        "num_attempts": 0,
        "site": "dmd26->(mx1|mx2).hc5801-97.iphmx.com@smtp_client",
        "tls_peer_subject_name": [
            "C=US",
            "ST=California",
            "L=San Jose",
            "O=Cisco Systems Inc.",
            "CN=mx1.hc5801-97.iphmx.com"
        ],
        "response": {
            "code": 503,
            "command": "DATA\r\n",
            "content": "#5.5.1 RCPT first"
        },
        "recipient": "xxxxx@f5.com",
        "created": 1748428117,
        "reception_protocol": "ESMTP",
        "source_address": {
            "protocol": "socks5",
            "address": "xxxxxxx:47005",
            "server": "10.168.20.50:6000"
        }
    }
]
3

Kumo version:Release 2025.05.06-b29689af

4

Simple Mail Transfer Protocol (SMTP) Enhanced Status Codes Registry said Invalid command
A mail transaction protocol command was issued which was either out of sequence or unsupported. This is useful only as a permanent error.
or
A valid mail transaction protocol command was issued with invalid arguments, either because the arguments were out of range or represented unrecognized features. This is useful only as a permanent error.

Is there a problem with the order in which KUMOMTA is sent to f5.com or is the upstream system call KUMOMTA?

If it is the latter, retry should solve the problem. But Now, retry is all failed.

5

I also get some error messages from /opt/kumomta/sbin/tailer --tail /var/log/kumomta

6

https://gist.github.com/smsvip/6994adef89704bab3f68e466aabb888c

7

As the error says, protocol sync issue. As it’s only with this domain I’d say it’s on them, not KumoMTA. I’d suggest setting the max deliveries per connection for that domain to 1 and see if it helps.

8

Even if only one email sent for this email domain in all kumo node? i will try max deliveres ,thank you.

9

Without a client trace there’s no way to know for sure.

10

https://gist.github.com/smsvip/6994adef89704bab3f68e466aabb888c this is system error log , yeah i have no client trace . in production environment i have no idea to resent this email

11

It’s a single domain, you can filter the client trace to that domain, then send a generic message? It will likely error again.

12

It is most likely that it is a problem with the recipient’s email. I used my personal gmail to send him an email on Gmail.com, which is the same error.

I was affected by the error log (Probable protocol synchronization error, please report this! Session ID=841c9fb8-e19a-4d39-9057-393bd79293fa), and I was fedback to KUMOMTA here, sorry.

13

Keep in mind you can use this to rewrite the response to be temporary instead of permanent: Rewriting Remote Server Responses - KumoMTA Docs

14

Thanks