[Bug]: Facing issue PLAIN TEXT authenticate method of SMTP

[brunopons]

⚠️ This issue respects the following points: ⚠️

• This is a bug, not a question or a configuration issue.
• This issue is not already reported on Github (I've searched it).

Bug description

Hello Guys, we are experiencing an inability to authenticate in clear text using the PLAIN or LOGIN method of SMTP on an internal Postfix server that only supports these two methods.

Have you ever faced this issue in the past? We were able to connect to other external email providers without any problems, the issue only resides on our internal network.

I captured tcp traffic that provide me this smtp sequence on every test ( client exits after receiving the server's capabilities ) :
220 smtp.randomzone.net ESMTP Postfix

EHLO a3efa1e49823

250-smtp.randomzone.net
250-PIPELINING
250-SIZE 20480000
250-VRFY
250-ETRN
250-AUTH LOGIN PLAIN
250-AUTH=LOGIN PLAIN
250-ENHANCEDSTATUSCODES
250-8BITMIME
250 DSN

QUIT

221 2.0.0 Bye

Steps to reproduce

1.configure sftp with our smtp server on port 25 with credentials
2.Select PLAIN or LOGIN Method and no Encryption
3.Send email to someone with test button

Expected behavior

SMTP Client authenticate and mail sending

SFTPGo version

v2.6.6

Data provider

https://github.com/drakkan

Installation method

Community Docker image

Configuration

docker-compose.yml sample:
...
environment:
TZ: "Europe/Paris"
SFTPGO_DATA_PROVIDER__CREATE_DEFAULT_ADMIN: 'true'
SFTPGO_DEFAULT_ADMIN_USERNAME: "{{ secrets['admin_username'] }}"
SFTPGO_DEFAULT_ADMIN_PASSWORD: "{{ secrets['admin_password'] }}"
SFTPGO_TELEMETRY__BIND_ADDRESS: '0.0.0.0'
SFTPGO_TELEMETRY__BIND_PORT: '10000'
SFTPGO_SMTP__HOST: 'smtp.randomzone.net'
SFTPGO_SMTP__PORT: '25'
SFTPGO_SMTP__FROM: '[email protected]'
SFTPGO_SMTP__USER: '[email protected]'
SFTPGO_SMTP__PASSWORD: "{{ secrets['smtp_password'] }}"
SFTPGO_SMTP__AUTH_TYPE: '0'
SFTPGO_SMTP__ENCRYPTION: '0'
SFTPGO_SMTP__DOMAIN: ''
...

Relevant log output

What are you using SFTPGo for?

Enterprise, Medium business

Additional info

No response