SMTP Test fails with "The specified string is not in the form required for an e-mail address" on v2.6.1.2 - even with valid email addresses

[Tedion]

Version: 2.6.1.2 (Docker)

Description:
The SMTP test button always fails with "The specified string is not in the form required for an e-mail address" regardless of the email address used in the Username field.

Tested with multiple valid email addresses:

All produce the same error. The CONFIRM button is disabled until the test passes, making it impossible to configure SMTP notifications.

This appears related to Issue #94 which was reportedly fixed, but the issue persists in 2.6.1.2.

Steps to reproduce:

1. Go to Settings → Notifications → SMTP Settings
2. Enter any valid email as Username
3. Fill in Password, Server (smtp.office365.com), Port (587)
4. Click TESTING
5. Error: "The specified string is not in the form required for an e-mail address"

Expected: Test should attempt SMTP connection and send a test email.

Environment: Docker deployment behind Nginx reverse proxy, Ubuntu.