Enhanced status code Success

SMTP error X.2.1

Mailbox disabled

Updated Jul 1, 2026

The short answer

Mailbox disabled Common cause: Recipient mailbox exists but is not accepting mail

Quick fix

Wait if temporary or contact the recipient another way

2 - Success. Not an error - the server accepted or completed the action.
This code is written X.2.1 because the reason is the same whether the failure is temporary (a 4 first digit) or permanent (a 5). Read the first digit of your own bounce to know which applies.

How to fix it

Wait if temporary or contact the recipient another way

Related codes

X.2.0 Other or undefined mailbox status X.2.2 Mailbox full X.2.3 Message length exceeds mailbox limit X.2.4 Mailing list expansion problem
All SMTP error codes
Ready when you are

Most rejections come back to sender reputation.

Blocklists, auth failures, and policy blocks are what warmup prevents. Warm up your domain so your mail is trusted before you hit send.

Start 7-day free trial Book a demo
7-day free trialNo credit cardCancel anytime