Use this SMTP AUTH PLAIN encoder to generate the base64 string used in AUTH PLAIN login flows for SMTP and IMAP.

What AUTH PLAIN encodes

AUTH PLAIN encodes the byte sequence:

  • NUL + username + NUL + password

That sequence is then base64-encoded and sent to the server. This tool shows both the concatenated representation and the encoded output so you can verify what your client is sending.

How to use this encoder

  1. Enter the username (often the full email address)
  2. Enter the password or app password
  3. Copy the Base64 encoded value into your mail client or compare it with debug logs

Security notes

  • Treat the base64 output like a password. Anyone with it can authenticate.
  • Prefer app passwords or scoped credentials when available.
  • Avoid pasting real credentials into shared tickets, screenshots, or public issue trackers.