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455

Server Unable to Accept

The server is temporarily unable to accommodate your request. Try again later.

What does this error mean?

SMTP error 455 indicates temporary server limitations:

  • Server is at maximum connection capacity
  • Resource constraints prevent processing
  • Temporary policy restriction
  • Server maintenance or updates

Common Causes

  • memory
    Resource Exhaustion

    The server has run out of memory or processing capacity.

  • lan
    Connection Limit

    Maximum number of simultaneous connections reached.

  • settings
    Configuration Limit

    Server configuration temporarily prevents accepting certain parameters.

    • How to Fix

    1. Wait and Retry

    This is almost always temporary. Your mail server will automatically retry delivery.

    2. Reduce Connection Load

    If sending bulk mail, reduce the number of simultaneous connections to this server.

    3. Check Server Status

    The recipient's mail provider may have posted maintenance notifications.

    Example response 
    455 4.3.0 Server unable to accommodate
455 Resources temporarily unavailable
455 4.7.1 Unable to accept parameters at this time

    Related SMTP Errors

    421 Service Not Available 451 Local Error 452 Insufficient Storage 450 Mailbox Unavailable

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