SMTP Checker 2026

Simple Windows user interface to validate SMTP credentials and optionally send a test email to selected recipients. Multi-threaded verification, progress display, and automatic saving of valid results.

### Features – **SMTP List Entry**: `HOST|PORT|USER|PASS` per line – **Recipient Management**: add, delete, load, save, select multiple recipients – **Login-only mode**: check credentials without sending email – **Sending Emails**: subject/sender/content with optional randomization – **Threading and Timeout Controls** – **Real-time Logs and Progress** – **Output Files**: `valid.txt` and `valid_logins.txt` – **Web Monitoring**: auto-pause in offline mode, auto-resume on return ### System Requirements – **OS**: Windows 10/11 – **Python**: 3.8 or later (tkinter is included in the standard Windows installer) ### Getting Started 1. **Download/Clone** this folder to your computer. 2. (Optional) Create a virtual environment: "`bash python -m venv .venv .venv\\Scripts\\activate "` 3. **Run the application**: "`bash python main.py "` ### Using the application 1. **SMTP List** – Paste or click "Load SMTP List" to import a ".txt" file. – Expected format per line: `HOST|PORT|USER|PASS` – Example: "` smtp.gmail.com|587|[email protected]|app-password smtp.mail.yahoo.com|587|[email protected]|password123

2. **Recipients** – Add recipients manually or use the "Load Recipients" option to import a JSON list. – Select one or more recipients from the list before starting (unless you are using login only). 3. **Settings** – **Login Only**: Authentication only; no email will be sent. – **Show password in log and email**: Enables or disables the inclusion of the raw SMTP string in the message content. – **Random**: Random subject, sender name, or content for each send. – **Threads**: Number of simultaneous SMTP checks. – **Delay**: Pause time between checks (in seconds). 4. **Compose** – Set the subject, sender name, and email content (HTML supported). 5. **Run** – Click **Start** to begin, **Pause/Resume**, or **Stop** at any time. – Progress and results are displayed in the log area. ### Output Files – **valid.txt**: Successful login and email sending credentials. – **valid_logins.txt**: Successful login credentials when "Verify login only" is enabled. – **recipients.json**: Automatically persisted when you add/remove recipients in the UI. ### Important Notes Regarding SMTP – The verifier uses "STARTTLS" (TLS upgrade) after EHLO. Make sure the selected port supports it (usually 587). – SMTPS on port 465 (implicit SSL) is not supported by this script. ### Troubleshooting – **"No recipients selected"**: Select at least one recipient from the list or enable "Verify login only". – **"Invalid SMTP format"**: Make sure each line is accurate. `HOST|PORT|USER|PASS` without spaces. – **Nothing happens / no progress**: – Check your internet connection; the application automatically pauses when offline. – Try reducing threads and increasing the timeout to avoid rate limits. – Some providers limit or block test messages; check the provider's policy. – **Authentication succeeds but sending fails**: The account may be allowed to connect but blocked from sending; check the provider's SMTP policies and application passwords. ### License This project is provided as-is, without warranty. Use it responsibly and in accordance with your provider's email terms and applicable laws.