SMTP: LOGIN authentication failed (STARTTLS/plaintext): sasl: unexpected server challenge

Question and Answers
1

Hi there:

We are experiencing SMTP authentication failures when using Custom Authentication:
Username and password are correct: IMAP Auth works.

Full Error Response:

{

“request_id”: “1205098503-4a7a663f-368a-4881-824a-7ba423a95a1c”,

“error”: {

"type": "grant.invalid_authentication",

"message": "Wrong SMTP username or password provided",

"provider_error": {

  "error": "LOGIN authentication failed (STARTTLS/plaintext): sasl: unexpected server challenge",

  "error_type": "authentication_failed"

}

}

}

Status:

- IMAP authentication: :white_check_mark: WORKS (same credentials)

- SMTP authentication: :cross_mark: FAILS with SASL error

2

Hello Nils,

We’ve confirmed that this behavior is indeed a bug. The issue has been escalated to our Engineering team for further investigation. I have reached out to you via email, once engineeing has an update expect a follow up via the email.

Best

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