SMTP 535 Authentication Failed vs 552 Exceeded Storage
Both SMTP 535 (Authentication Failed) and 552 (Exceeded Storage) belong to the 5xx Permanent Negative category. 535 indicates that the authentication credentials provided are invalid. The username, password, or authentication mechanism was rejected by the server. Meanwhile, 552 means that the requested mail action was aborted because the recipient's mailbox has exceeded its storage allocation. Unlike the temporary 452, this is a permanent rejection for this specific mailbox.
Description
The authentication credentials provided are invalid. The username, password, or authentication mechanism was rejected by the server.
When You See It
After submitting incorrect credentials via the AUTH command. The username or password does not match any account on the server.
How to Fix
Double-check your username and password. If using an app password (e.g., Gmail, Outlook), ensure it is current and has not been revoked. Also verify the correct SASL mechanism (PLAIN, LOGIN, etc.).
Description
The requested mail action was aborted because the recipient's mailbox has exceeded its storage allocation. Unlike the temporary 452, this is a permanent rejection for this specific mailbox.
When You See It
When the recipient's mailbox is completely full and cannot accept any more messages. The recipient needs to delete old emails or increase their quota.
How to Fix
Notify the recipient through another channel that their mailbox is full. If you are the recipient, delete old messages or contact your mail administrator to increase the storage quota.
Key Differences
SMTP 535: The authentication credentials provided are invalid. The username, password, or authentication mechanism was rejected by the server.
SMTP 552: The requested mail action was aborted because the recipient's mailbox has exceeded its storage allocation. Unlike the temporary 452, this is a permanent rejection for this specific mailbox.
You encounter 535 when after submitting incorrect credentials via the AUTH command. The username or password does not match any account on the server.
You encounter 552 when when the recipient's mailbox is completely full and cannot accept any more messages. The recipient needs to delete old emails or increase their quota.
When to Use Which
For 535 (Authentication Failed): Double-check your username and password. If using an app password (e.g., Gmail, Outlook), ensure it is current and has not been revoked. Also verify the correct SASL mechanism (PLAIN, LOGIN, etc.). For 552 (Exceeded Storage): Notify the recipient through another channel that their mailbox is full. If you are the recipient, delete old messages or contact your mail administrator to increase the storage quota.