Recoverable error.
This message is returned to the mail client from the local host when the mail server has detected a pacing problem and the mail cannot be delivered. SMTP protocol dictates that the SMTP client should wait for a reply from the SMTP server before sending the next SMTP command (for example, RCPT). Pacing problems cause the client and server communications to get out of synchronization.
SMTP continues.
Notify the owner of remote SMTP client of the problem.
SMTPCMDS
StoreData