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Basic SMTP reply code · RFC 5321

534 Authentication mechanism too weak

A reply to AUTH: the chosen mechanism is weaker than the server's policy allows; the client must pick another (RFC 4954).

Class: 5yz · Permanent failure
5yz: a permanent failure. The same request should not be repeated; something must change first, such as the address (RFC 5321 §4.2.1).
Associated enhanced codes
The enhanced codes that usually come with this code, per the registry and the providers:

5.7.95.7.145.7.90
Source
RFC 4954

How 534 appears at providers

The exact text from the provider's documentation, as you see it in the bounce, and what it means.

Gmail

534 5.7.14Please log in through your web browser and then try again.

Google wants a login through the web browser before the application can send.
534 5.7.90Application-specific password required.

The account needs an app password for this mail client.
534 5.7.90Please log in with your web browser and then try again.

Google wants a login through the web browser before the application can send.

Have the whole error message?

Sources: RFC 5321 · RFC 3463 · RFC 3464 · IANA · Gmail · Microsoft 365 · read on 26 September 2026