office.com Starting TLS handshake and then disconnected

[jaccky]

Hi,
I've tryed to setup the proxy with Client Credentials Flow to smtp.outlook.com
This is my configurations:

---

[SMTP-2465]
server_address = smtp.outlook.com
server_port = 587
server_starttls = True
local_address = 127.0.0.1

[accounts-XXXXX@customdomain.com]
#documentation = *** note: this is an advanced O365 account example; in most cases you want the version above instead ***
token_url = https://login.microsoftonline.com/8f37d23c-8237-447d-8298-a223ad163ff4/oauth2/v2.0/token
oauth2_scope = https://outlook.office.com/SMTP.Send offline_access
oauth2_flow = client_credentials
client_id = XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
client_secret = XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX

---

And this the log with debug output:

2025-08-01 11:12:59: New incoming connection to SMTP server at 127.0.0.1:2465 (unsecured) proxying smtp.outlook.com:587 (STARTTLS)
2025-08-01 11:12:59: Accepting new connection from 127.0.0.1:53618 to SMTP server at 127.0.0.1:2465 (unsecured) proxying smtp.outlook.com:587 (STARTTLS)
2025-08-01 11:12:59: SMTP (127.0.0.1:53618-{127.0.0.1:2465}-smtp.outlook.com:587) --> [ Client connected ]
2025-08-01 11:13:00: SMTP (127.0.0.1:53618-{127.0.0.1:2465}-smtp.outlook.com:587)     <-- b'220 ZR0P278CA0081.outlook.office365.com Microsoft ESMTP MAIL Service ready at Fri, 1 Aug 2025 09:12:51 +0000 [08DDCF8353751293]\r\n'
2025-08-01 11:13:00: SMTP (127.0.0.1:53618-{127.0.0.1:2465}-smtp.outlook.com:587) <-- b'220 ZR0P278CA0081.outlook.office365.com Microsoft ESMTP MAIL Service ready at Fri, 1 Aug 2025 09:12:51 +0000 [08DDCF8353751293]\r\n'
2025-08-01 11:13:00: SMTP (127.0.0.1:53618-{127.0.0.1:2465}-smtp.outlook.com:587) --> b'EHLO gewissisdb\r\n'
2025-08-01 11:13:00: SMTP (127.0.0.1:53618-{127.0.0.1:2465}-smtp.outlook.com:587)     --> b'EHLO gewissisdb\r\n'
2025-08-01 11:13:00: SMTP (127.0.0.1:53618-{127.0.0.1:2465}-smtp.outlook.com:587)     <-- b'250-ZR0P278CA0081.outlook.office365.com Hello [128.251.157.81]\r\n'
2025-08-01 11:13:00: SMTP (127.0.0.1:53618-{127.0.0.1:2465}-smtp.outlook.com:587)     <-- b'250-SIZE 157286400\r\n'
2025-08-01 11:13:00: SMTP (127.0.0.1:53618-{127.0.0.1:2465}-smtp.outlook.com:587)     <-- b'250-PIPELINING\r\n'
2025-08-01 11:13:00: SMTP (127.0.0.1:53618-{127.0.0.1:2465}-smtp.outlook.com:587)     <-- b'250-DSN\r\n'
2025-08-01 11:13:00: SMTP (127.0.0.1:53618-{127.0.0.1:2465}-smtp.outlook.com:587)     <-- b'250-ENHANCEDSTATUSCODES\r\n'
2025-08-01 11:13:00: SMTP (127.0.0.1:53618-{127.0.0.1:2465}-smtp.outlook.com:587)     <-- b'250-STARTTLS\r\n'
2025-08-01 11:13:00: SMTP (127.0.0.1:53618-{127.0.0.1:2465}-smtp.outlook.com:587)     <-- b'250-8BITMIME\r\n'
2025-08-01 11:13:00: SMTP (127.0.0.1:53618-{127.0.0.1:2465}-smtp.outlook.com:587)     <-- b'250-BINARYMIME\r\n'
2025-08-01 11:13:00: SMTP (127.0.0.1:53618-{127.0.0.1:2465}-smtp.outlook.com:587)     <-- b'250-CHUNKING\r\n'
2025-08-01 11:13:00: SMTP (127.0.0.1:53618-{127.0.0.1:2465}-smtp.outlook.com:587)     <-- b'250 SMTPUTF8\r\n'
2025-08-01 11:13:00: SMTP (127.0.0.1:53618-{127.0.0.1:2465}-smtp.outlook.com:587)     --> b'STARTTLS\r\n'
2025-08-01 11:13:00: SMTP (127.0.0.1:53618-{127.0.0.1:2465}-smtp.outlook.com:587)     <-- b'220 2.0.0 SMTP server ready\r\n'
2025-08-01 11:13:00: SMTP (127.0.0.1:53618-{127.0.0.1:2465}-smtp.outlook.com:587) <-> [ Starting TLS handshake ]
2025-08-01 11:13:00: SMTP (127.0.0.1:53618-{127.0.0.1:2465}-smtp.outlook.com:587) Caught server exception in subclass; client connection closed before data could be sent
2025-08-01 11:13:00: SMTP (127.0.0.1:53618-{127.0.0.1:2465}-smtp.outlook.com:587) <-- [ Server disconnected ]
2025-08-01 11:13:00: SMTP (127.0.0.1:53618-{127.0.0.1:2465}-smtp.outlook.com:587) --> [ Client disconnected ]

As you can see suddendly after TLS handshake, the server disconnects, there is no trace of oauth authentication attempt or else.
Any idea on how to further debug this ?

Many thanks wor your work,
Gian.

[simonrob]

What operating system and Python version are you using? (If a precompiled version of the proxy, which one?)

[AS-SH]

potentially the same issue here, deviation from Gian's problem, the stop occure after TLS handshake commplete:

2025-08-02 12:11:41: SMTP (192.168.0.17:60524-{192.168.0.100:1587}-smtp.office365.com:587) <-- b'250-FR0P281CA0110.outlook.office365.com Hello [2a02:8106:22a:3700:4990:27c8:e121:c1e8]\r\n250-SIZE 157286400\r\n250-PIPELINING\r\n250-DSN\r\n250-ENHANCEDSTATUSCODES\r\n250-AUTH PLAIN LOGIN\r\n250-8BITMIME\r\n250-BINARYMIME\r\n250-CHUNKING\r\n250 SMTPUTF8\r\n'
2025-08-02 12:11:41: SMTP (192.168.0.17:60524-{192.168.0.100:1587}-smtp.office365.com:587) --> [ Client disconnected ]
2025-08-02 12:11:41: SMTP (192.168.0.17:60524-{192.168.0.100:1587}-smtp.office365.com:587) <-- [ Server disconnected ]

Win Server 2019; Python 3.11.6

[simonrob]

Do you get the same issue if you connect using telnet as outlined in the readme? And, if you're not using a pre-compiled version of the proxy, have you tried pip install certifi?

[AS-SH]

telent response is different:

2025-08-04 13:15:30: New incoming connection to SMTP server at 192.168.0.100:1587 (unsecured) proxying smtp.office365.com:587 (STARTTLS)
2025-08-04 13:15:30: Accepting new connection from 192.168.0.231:61590 to SMTP server at 192.168.0.100:1587 (unsecured) proxying smtp.office365.com:587 (STARTTLS)
2025-08-04 13:15:30: SMTP (192.168.0.231:61590-{192.168.0.100:1587}-smtp.office365.com:587) --> [ Client connected ]
2025-08-04 13:15:30: SMTP (192.168.0.231:61590-{192.168.0.100:1587}-smtp.office365.com:587)     <-- b'220 BE1P281CA0440.outlook.office365.com Microsoft ESMTP MAIL Service ready at Mon, 4 Aug 2025 11:15:30 +0000 [08DDD30471EE4ED5]\r\n'
2025-08-04 13:15:30: SMTP (192.168.0.231:61590-{192.168.0.100:1587}-smtp.office365.com:587) <-- b'220 BE1P281CA0440.outlook.office365.com Microsoft ESMTP MAIL Service ready at Mon, 4 Aug 2025 11:15:30 +0000 [08DDD30471EE4ED5]\r\n'
2025-08-04 13:15:48: SMTP (192.168.0.231:61590-{192.168.0.100:1587}-smtp.office365.com:587) --> b'a1 login [[ Credentials removed from proxy log ]]\r\n'
2025-08-04 13:15:48: SMTP (192.168.0.231:61590-{192.168.0.100:1587}-smtp.office365.com:587)     --> b'a1 login xx@xxx.xx test\r\n'
2025-08-04 13:15:53: SMTP (192.168.0.231:61590-{192.168.0.100:1587}-smtp.office365.com:587)     <-- b"500 5.3.3 Unrecognized command 'Length: 2' [BE1P281CA0440.DEUP281.PROD.OUTLOOK.COM 2025-08-04T11:15:53.057Z 08DDD30471EE4ED5]\r\n"

Authorisation of the account wasn't started :(

Update: Usage of precompiled package stops at the same point, therefore problem is reproducable (unfortunately)

[jaccky]

Hi,
using python 3.6 on Red Hat Enterprise Linux Server release 7.9 (Maipo)
installed emailproxy 2024.5.25 using pip

[simonrob]

@AS-SH you're using an IMAP command with a SMTP server. For SMTP the login command is different: base64-encoded username and password separated by a null byte. The error shown in your log is only because of this, and not related to the original.

[jaccky]

I have the same issue when I try an smtp session connecting via telnet to the proxy:

[webadmin@gddwo2007a ~]$ telnet 127.0.0.1 2465
Trying 127.0.0.1...
Connected to 127.0.0.1.
Escape character is '^]'.
220 MI1P293CA0021.outlook.office365.com Microsoft ESMTP MAIL Service ready at Tue, 5 Aug 2025 10:40:22 +0000 [08DDD30FB59F032A]
EHLO idp.gewiss.com
Connection closed by foreign host.
[webadmin@gddwo2007a ~]$

---

This id the usual debug output of the proxy:

[webadmin@gddwo2007a ~]$ python3 -m emailproxy --no-gui --debug
/home/webadmin/.local/lib/python3.6/site-packages/emailproxy.py:55: CryptographyDeprecationWarning: Python 3.6 is no longer supported by the Python core team. Therefore, support for it is deprecated in cryptography. The next release of cryptography will remove support for Python 3.6.
  from cryptography.fernet import Fernet, MultiFernet, InvalidToken
2025-08-05 12:40:23: Initialising Email OAuth 2.0 Proxy (version 2024-05-25) in debug mode from config file /home/webadmin/emailproxy.config
2025-08-05 12:40:23: Starting SMTP server at 127.0.0.1:2465 (unsecured) proxying smtp.outlook.com:587 (STARTTLS)
2025-08-05 12:40:23: Initialised Email OAuth 2.0 Proxy - listening for authentication requests. Connect your email client to begin
2025-08-05 12:40:34: New incoming connection to SMTP server at 127.0.0.1:2465 (unsecured) proxying smtp.outlook.com:587 (STARTTLS)
2025-08-05 12:40:34: Accepting new connection from 127.0.0.1:43690 to SMTP server at 127.0.0.1:2465 (unsecured) proxying smtp.outlook.com:587 (STARTTLS)
2025-08-05 12:40:34: SMTP (127.0.0.1:43690-{127.0.0.1:2465}-smtp.outlook.com:587) --> [ Client connected ]
2025-08-05 12:40:34: SMTP (127.0.0.1:43690-{127.0.0.1:2465}-smtp.outlook.com:587)     <-- b'220 MI1P293CA0021.outlook.office365.com Microsoft ESMTP MAIL Service ready at Tue, 5 Aug 2025 10:40:22 +0000 [08DDD30FB59F032A]\r\n'
2025-08-05 12:40:34: SMTP (127.0.0.1:43690-{127.0.0.1:2465}-smtp.outlook.com:587) <-- b'220 MI1P293CA0021.outlook.office365.com Microsoft ESMTP MAIL Service ready at Tue, 5 Aug 2025 10:40:22 +0000 [08DDD30FB59F032A]\r\n'
2025-08-05 12:40:45: SMTP (127.0.0.1:43690-{127.0.0.1:2465}-smtp.outlook.com:587) --> b'EHLO idp.gewiss.com\r\n'
2025-08-05 12:40:45: SMTP (127.0.0.1:43690-{127.0.0.1:2465}-smtp.outlook.com:587)     --> b'EHLO idp.gewiss.com\r\n'
2025-08-05 12:40:45: SMTP (127.0.0.1:43690-{127.0.0.1:2465}-smtp.outlook.com:587)     <-- b'250-MI1P293CA0021.outlook.office365.com Hello [128.251.157.81]\r\n'
2025-08-05 12:40:45: SMTP (127.0.0.1:43690-{127.0.0.1:2465}-smtp.outlook.com:587)     <-- b'250-SIZE 157286400\r\n'
2025-08-05 12:40:45: SMTP (127.0.0.1:43690-{127.0.0.1:2465}-smtp.outlook.com:587)     <-- b'250-PIPELINING\r\n'
2025-08-05 12:40:45: SMTP (127.0.0.1:43690-{127.0.0.1:2465}-smtp.outlook.com:587)     <-- b'250-DSN\r\n'
2025-08-05 12:40:45: SMTP (127.0.0.1:43690-{127.0.0.1:2465}-smtp.outlook.com:587)     <-- b'250-ENHANCEDSTATUSCODES\r\n'
2025-08-05 12:40:45: SMTP (127.0.0.1:43690-{127.0.0.1:2465}-smtp.outlook.com:587)     <-- b'250-STARTTLS\r\n'
2025-08-05 12:40:45: SMTP (127.0.0.1:43690-{127.0.0.1:2465}-smtp.outlook.com:587)     <-- b'250-8BITMIME\r\n'
2025-08-05 12:40:45: SMTP (127.0.0.1:43690-{127.0.0.1:2465}-smtp.outlook.com:587)     <-- b'250-BINARYMIME\r\n'
2025-08-05 12:40:45: SMTP (127.0.0.1:43690-{127.0.0.1:2465}-smtp.outlook.com:587)     <-- b'250-CHUNKING\r\n'
2025-08-05 12:40:45: SMTP (127.0.0.1:43690-{127.0.0.1:2465}-smtp.outlook.com:587)     <-- b'250 SMTPUTF8\r\n'
2025-08-05 12:40:45: SMTP (127.0.0.1:43690-{127.0.0.1:2465}-smtp.outlook.com:587)     --> b'STARTTLS\r\n'
2025-08-05 12:40:45: SMTP (127.0.0.1:43690-{127.0.0.1:2465}-smtp.outlook.com:587)     <-- b'220 2.0.0 SMTP server ready\r\n'
2025-08-05 12:40:45: SMTP (127.0.0.1:43690-{127.0.0.1:2465}-smtp.outlook.com:587) <-> [ Starting TLS handshake ]
2025-08-05 12:40:45: SMTP (127.0.0.1:43690-{127.0.0.1:2465}-smtp.outlook.com:587) Caught server exception in subclass; client connection closed before data could be sent
2025-08-05 12:40:45: SMTP (127.0.0.1:43690-{127.0.0.1:2465}-smtp.outlook.com:587) <-- [ Server disconnected ]
2025-08-05 12:40:45: SMTP (127.0.0.1:43690-{127.0.0.1:2465}-smtp.outlook.com:587) --> [ Client disconnected ]

[simonrob]

Since I can't replicate this I can only assume there is some TLS issue with your client. It's also worth upgrading Python to 3.7 since 3.6 is not officially supported.

[jaccky]

I confirm it was a Python version problem, I switched to a newer Python 3.8 and now the "after TLS handshake disconnection" problem seems to be solved.

Anyway the authentication doesn't work:

2025-08-05 15:59:33: New incoming connection to SMTP server at 127.0.0.1:2465 (unsecured) proxying smtp-legacy.office365.com:587 (STARTTLS)
2025-08-05 15:59:33: Accepting new connection from 127.0.0.1:40584 to SMTP server at 127.0.0.1:2465 (unsecured) proxying smtp-legacy.office365.com:587 (STARTTLS)
2025-08-05 15:59:33: SMTP (127.0.0.1:40584-{127.0.0.1:2465}-smtp-legacy.office365.com:587) --> [ Client connected ]
2025-08-05 15:59:33: SMTP (127.0.0.1:40584-{127.0.0.1:2465}-smtp-legacy.office365.com:587)     <-- b'220 MI1P293CA0009.outlook.office365.com Microsoft ESMTP MAIL Service ready at Tue, 5 Aug 2025 13:59:21 +0000 [08DDD40205B1BA7C]\r\n'
2025-08-05 15:59:33: SMTP (127.0.0.1:40584-{127.0.0.1:2465}-smtp-legacy.office365.com:587) <-- b'220 MI1P293CA0009.outlook.office365.com Microsoft ESMTP MAIL Service ready at Tue, 5 Aug 2025 13:59:21 +0000 [08DDD40205B1BA7C]\r\n'
2025-08-05 15:59:33: SMTP (127.0.0.1:40584-{127.0.0.1:2465}-smtp-legacy.office365.com:587) --> b'EHLO gewissisdb\r\n'
2025-08-05 15:59:33: SMTP (127.0.0.1:40584-{127.0.0.1:2465}-smtp-legacy.office365.com:587)     --> b'EHLO gewissisdb\r\n'
2025-08-05 15:59:33: SMTP (127.0.0.1:40584-{127.0.0.1:2465}-smtp-legacy.office365.com:587)     <-- b'250-MI1P293CA0009.outlook.office365.com Hello [128.251.157.81]\r\n'
2025-08-05 15:59:33: SMTP (127.0.0.1:40584-{127.0.0.1:2465}-smtp-legacy.office365.com:587)     <-- b'250-SIZE 157286400\r\n'
2025-08-05 15:59:33: SMTP (127.0.0.1:40584-{127.0.0.1:2465}-smtp-legacy.office365.com:587)     <-- b'250-PIPELINING\r\n'
2025-08-05 15:59:33: SMTP (127.0.0.1:40584-{127.0.0.1:2465}-smtp-legacy.office365.com:587)     <-- b'250-DSN\r\n'
2025-08-05 15:59:33: SMTP (127.0.0.1:40584-{127.0.0.1:2465}-smtp-legacy.office365.com:587)     <-- b'250-ENHANCEDSTATUSCODES\r\n'
2025-08-05 15:59:33: SMTP (127.0.0.1:40584-{127.0.0.1:2465}-smtp-legacy.office365.com:587)     <-- b'250-STARTTLS\r\n'
2025-08-05 15:59:33: SMTP (127.0.0.1:40584-{127.0.0.1:2465}-smtp-legacy.office365.com:587)     <-- b'250-8BITMIME\r\n'
2025-08-05 15:59:33: SMTP (127.0.0.1:40584-{127.0.0.1:2465}-smtp-legacy.office365.com:587)     <-- b'250-BINARYMIME\r\n'
2025-08-05 15:59:33: SMTP (127.0.0.1:40584-{127.0.0.1:2465}-smtp-legacy.office365.com:587)     <-- b'250-CHUNKING\r\n'
2025-08-05 15:59:33: SMTP (127.0.0.1:40584-{127.0.0.1:2465}-smtp-legacy.office365.com:587)     <-- b'250 SMTPUTF8\r\n'
2025-08-05 15:59:33: SMTP (127.0.0.1:40584-{127.0.0.1:2465}-smtp-legacy.office365.com:587)     --> b'STARTTLS\r\n'
2025-08-05 15:59:33: SMTP (127.0.0.1:40584-{127.0.0.1:2465}-smtp-legacy.office365.com:587)     <-- b'220 2.0.0 SMTP server ready\r\n'
2025-08-05 15:59:33: SMTP (127.0.0.1:40584-{127.0.0.1:2465}-smtp-legacy.office365.com:587) <-> [ Starting TLS handshake ]
2025-08-05 15:59:33: SMTP (127.0.0.1:40584-{127.0.0.1:2465}-smtp-legacy.office365.com:587) [ Successfully negotiated SMTP server STARTTLS connection - re-sending greeting ]
2025-08-05 15:59:33: SMTP (127.0.0.1:40584-{127.0.0.1:2465}-smtp-legacy.office365.com:587)     --> b'EHLO gewissisdb\r\n'
2025-08-05 15:59:33: SMTP (127.0.0.1:40584-{127.0.0.1:2465}-smtp-legacy.office365.com:587) <-> [ TLSv1.2 handshake complete ]
2025-08-05 15:59:33: SMTP (127.0.0.1:40584-{127.0.0.1:2465}-smtp-legacy.office365.com:587)     <-- b'250-MI1P293CA0009.outlook.office365.com Hello [128.251.157.81]\r\n'
2025-08-05 15:59:33: SMTP (127.0.0.1:40584-{127.0.0.1:2465}-smtp-legacy.office365.com:587)     <-- b'250-SIZE 157286400\r\n'
2025-08-05 15:59:33: SMTP (127.0.0.1:40584-{127.0.0.1:2465}-smtp-legacy.office365.com:587)     <-- b'250-PIPELINING\r\n'
2025-08-05 15:59:33: SMTP (127.0.0.1:40584-{127.0.0.1:2465}-smtp-legacy.office365.com:587)     <-- b'250-DSN\r\n'
2025-08-05 15:59:33: SMTP (127.0.0.1:40584-{127.0.0.1:2465}-smtp-legacy.office365.com:587)     <-- b'250-ENHANCEDSTATUSCODES\r\n'
2025-08-05 15:59:33: SMTP (127.0.0.1:40584-{127.0.0.1:2465}-smtp-legacy.office365.com:587)     <-- b'250-AUTH LOGIN XOAUTH2\r\n'
2025-08-05 15:59:33: SMTP (127.0.0.1:40584-{127.0.0.1:2465}-smtp-legacy.office365.com:587)     <-- b'250-8BITMIME\r\n'
2025-08-05 15:59:33: SMTP (127.0.0.1:40584-{127.0.0.1:2465}-smtp-legacy.office365.com:587)     <-- b'250-BINARYMIME\r\n'
2025-08-05 15:59:33: SMTP (127.0.0.1:40584-{127.0.0.1:2465}-smtp-legacy.office365.com:587)     <-- b'250-CHUNKING\r\n'
2025-08-05 15:59:33: SMTP (127.0.0.1:40584-{127.0.0.1:2465}-smtp-legacy.office365.com:587)     <-- b'250 SMTPUTF8\r\n'
2025-08-05 15:59:33: SMTP (127.0.0.1:40584-{127.0.0.1:2465}-smtp-legacy.office365.com:587) <-- b'250-MI1P293CA0009.outlook.office365.com Hello [128.251.157.81]\r\n250-SIZE 157286400\r\n250-PIPELINING\r\n250-DSN\r\n250-ENHANCEDSTATUSCODES\r\n250-AUTH PLAIN LOGIN\r\n250-8BITMIME\r\n250-BINARYMIME\r\n250-CHUNKING\r\n250 SMTPUTF8\r\n'
2025-08-05 15:59:33: SMTP (127.0.0.1:40584-{127.0.0.1:2465}-smtp-legacy.office365.com:587) --> b'AUTH LOGIN\r\n'
2025-08-05 15:59:33: SMTP (127.0.0.1:40584-{127.0.0.1:2465}-smtp-legacy.office365.com:587) <-- b'334 VXNlcm5hbWU6\r\n'
2025-08-05 15:59:33: SMTP (127.0.0.1:40584-{127.0.0.1:2465}-smtp-legacy.office365.com:587) --> b'YWNjb3VudHMtMjQxMjA5QGdld2lzcy5jb20=\r\n'
2025-08-05 15:59:33: SMTP (127.0.0.1:40584-{127.0.0.1:2465}-smtp-legacy.office365.com:587) <-- b'334 UGFzc3dvcmQ6\r\n'
2025-08-05 15:59:33: SMTP (127.0.0.1:40584-{127.0.0.1:2465}-smtp-legacy.office365.com:587) --> b'[[ Credentials removed from proxy log ]]'
2025-08-05 15:59:33: SMTP (127.0.0.1:40584-{127.0.0.1:2465}-smtp-legacy.office365.com:587) Caught asyncore info message (client) - error : uncaptured python exception, closing channel <__main__.SMTPOAuth2ClientConnection connected 127.0.0.1:40584 at 0x7fb580357250> (<class 'UnicodeDecodeError'>:'utf-8' codec can't decode byte 0xe8 in position 9: invalid continuation byte [/opt/rh/rh-python38/root/usr/lib64/python3.8/asyncore.py|read|83] [/home/webadmin/.local/lib/python3.8/site-packages/emailproxy.py|handle_read_event|1468] [/opt/rh/rh-python38/root/usr/lib64/python3.8/asyncore.py|handle_read_event|420] [/home/webadmin/.local/lib/python3.8/site-packages/emailproxy.py|handle_read|1607] [/home/webadmin/.local/lib/python3.8/site-packages/emailproxy.py|process_data|1946])
2025-08-05 15:59:33: SMTP (127.0.0.1:40584-{127.0.0.1:2465}-smtp-legacy.office365.com:587) Caught connection error (client) - UnicodeDecodeError : 'utf-8' codec can't decode byte 0xe8 in position 9: invalid continuation byte
2025-08-05 15:59:33: SMTP (127.0.0.1:40584-{127.0.0.1:2465}-smtp-legacy.office365.com:587) --> [ Client disconnected ]
2025-08-05 15:59:33: SMTP (127.0.0.1:40584-{127.0.0.1:2465}-smtp-legacy.office365.com:587) <-- [ Server disconnected ]

[simonrob]

This is probably because you have for some reason switched to smtp-legacy.office365.com. The proxy doesn't support legacy TLS versions. Change back to the standard configuration as given in the example configuration file and it will work.

[simonrob]

I'm going to assume this is now resolved and close this issue, but feel free to reopen if not.