554 5.5.0 Error: SMTP protocol synchronization

nginx

HTTP/1.1 301 Moved Permanently
Server: nginx
Date: Sat, 08 Feb 2025 09:38:18 GMT
Content-Type: text/html
Content-Length: 162
Connection: keep-alive
Location: https://5.75.170.174/
X-Frame-Options: SAMEORIGIN
X-XSS-Protection: 1; mode=block
X-Content-Type-Options: nosniff
Referrer-Policy: no-referrer-when-downgrade
Content-Security-Policy: default-src * data: 'unsafe-eval' 'unsafe-inline'

nginx

Bridgeclub

HTTP/1.1 200 OK
Server: nginx
Date: Sat, 08 Feb 2025 10:09:41 GMT
Content-Type: text/html
Content-Length: 29414
Last-Modified: Sun, 03 Dec 2023 11:26:11 GMT
Connection: keep-alive
Vary: Accept-Encoding
ETag: "656c65d3-72e6"
X-Frame-Options: SAMEORIGIN
X-XSS-Protection: 1; mode=block
X-Content-Type-Options: nosniff
Referrer-Policy: no-referrer-when-downgrade
Content-Security-Policy: default-src * data: 'unsafe-eval' 'unsafe-inline'
Accept-Ranges: bytes

Certificate:
    Data:
        Version: 3 (0x2)
        Serial Number:
            04:5b:cb:b7:40:df:f1:5a:3f:a7:e1:14:79:93:fa:d7:6e:30
        Signature Algorithm: ecdsa-with-SHA384
        Issuer: C=US, O=Let's Encrypt, CN=E6
        Validity
            Not Before: Dec 30 15:13:36 2024 GMT
            Not After : Mar 30 15:13:35 2025 GMT
        Subject: CN=bridgesportclub.at
        Subject Public Key Info:
            Public Key Algorithm: id-ecPublicKey
                Public-Key: (256 bit)
                pub:
                    04:84:70:43:af:bf:ef:e7:93:ef:d6:4b:d5:25:10:
                    7f:0a:f7:00:03:c0:4b:b2:52:61:3d:45:b4:4e:5e:
                    e1:e4:b5:3f:6c:43:b9:71:58:80:53:42:a2:8f:b8:
                    12:f6:e9:d1:08:a4:b7:34:f5:b0:ea:2c:43:7a:3c:
                    d8:9c:d2:30:07
                ASN1 OID: prime256v1
                NIST CURVE: P-256
        X509v3 extensions:
            X509v3 Key Usage: critical
                Digital Signature
            X509v3 Extended Key Usage: 
                TLS Web Server Authentication, TLS Web Client Authentication
            X509v3 Basic Constraints: critical
                CA:FALSE
            X509v3 Subject Key Identifier: 
                D2:2C:A9:44:B1:7D:97:89:01:97:39:A6:0E:E8:B1:EF:AB:EF:FF:FB
            X509v3 Authority Key Identifier: 
                93:27:46:98:03:A9:51:68:8E:98:D6:C4:42:48:DB:23:BF:58:94:D2
            Authority Information Access: 
                OCSP - URI:http://e6.o.lencr.org
                CA Issuers - URI:http://e6.i.lencr.org/
            X509v3 Subject Alternative Name: 
                DNS:api.bridgesportclub.at, DNS:bridgesportclub.at, DNS:mail.bridgesportclub.at, DNS:www.bridgesportclub.at
            X509v3 Certificate Policies: 
                Policy: 2.23.140.1.2.1
            CT Precertificate SCTs: 
                Signed Certificate Timestamp:
                    Version   : v1 (0x0)
                    Log ID    : A2:E3:0A:E4:45:EF:BD:AD:9B:7E:38:ED:47:67:77:53:
                                D7:82:5B:84:94:D7:2B:5E:1B:2C:C4:B9:50:A4:47:E7
                    Timestamp : Dec 30 16:12:06.319 2024 GMT
                    Extensions: none
                    Signature : ecdsa-with-SHA256
                                30:45:02:21:00:E5:DB:F4:75:8B:57:52:C4:0B:80:42:
                                1C:4C:31:E8:41:3C:03:BC:5F:D8:62:7C:BF:7A:A9:AF:
                                4B:2D:1B:9B:14:02:20:1B:A0:97:1E:59:05:69:97:5B:
                                0E:8C:5C:31:A9:CE:30:A9:3B:48:49:25:3D:F4:57:12:
                                0E:CA:32:01:6F:5A:6D
                Signed Certificate Timestamp:
                    Version   : v1 (0x0)
                    Log ID    : E0:92:B3:FC:0C:1D:C8:E7:68:36:1F:DE:61:B9:96:4D:
                                0A:52:78:19:8A:72:D6:72:C4:B0:4D:A5:6D:6F:54:04
                    Timestamp : Dec 30 16:12:06.380 2024 GMT
                    Extensions: none
                    Signature : ecdsa-with-SHA256
                                30:45:02:21:00:AE:90:43:C3:A6:D4:C2:A6:D6:3D:C8:
                                D4:23:3C:16:72:63:8B:39:A3:D1:6F:08:18:C8:BA:E0:
                                F1:FC:08:FC:23:02:20:49:77:55:3B:06:82:F9:94:1A:
                                56:39:E0:71:12:19:4E:A3:C7:5C:31:B0:24:A4:FD:D4:
                                83:A8:C8:E8:C1:CB:90
    Signature Algorithm: ecdsa-with-SHA384
    Signature Value:
        30:66:02:31:00:81:e6:0f:5b:85:73:c0:65:e3:a1:0f:52:b6:
        d7:cc:79:97:94:5a:5e:e9:e5:7f:8e:6a:d8:42:23:7f:01:b0:
        64:45:fd:ce:c1:b8:8b:66:d9:cb:2a:18:95:c6:e1:29:9e:02:
        31:00:a7:7d:2e:08:f9:e6:c4:42:bb:7e:69:1c:8a:d5:f5:b2:
        10:6e:f4:e7:94:fa:d8:86:b8:f1:b1:25:b7:8e:8b:95:45:87:
        0c:c2:87:26:37:e2:fd:23:1c:e1:65:2a:4e:2f