450: Requested Action Not Taken (Temporary)

The 450 SMTP error is a temporary rejection often caused by greylisting. Learn what causes 450 errors and how your server handles retries.

Published · Last verified · Maintained by TamingDNS

🟡
Temporary Failure (Soft Bounce)
SMTP Code
450
Category
Requested Action Not Taken (Temporary)
Frequency
Common

💬 What This Error Means

The server is asking you to 'call back later.' This is usually a security trick called greylisting. By rejecting the first attempt, the server makes sure you're a real mail server and not a one-off spam bot.

Common Causes

  • Greylisting (the most common reason for a 450 error)
  • The recipient's inbox is temporarily busy or locked
  • The server is briefly out of resources

How to Fix This

  • Be patient. Your server will try again in 5-15 minutes and it should go through
  • If it still fails after an hour, the problem might be more than just a temporary hold

📚 Official Documentation

↗ RFC 5321: SMTP

📋 Real-World Example Messages

These are real bounce message formats you might receive. Paste yours into the Bounce Decoder for instant analysis. 

450 Requested mail action not taken: mailbox unavailable
450 Mailbox temporarily unavailable

🔗 Related Error Codes

450 4.2.1
Rate Limit: Try Again Later
451
Local Processing Error (Temporary)
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