Delay to send and receive emails due to "Server busy. Please try again later"Issue Email notifications correctly triggered and sent from the instance are received by users several hours later.CauseMail server logs show the message "Server Busy" on the user's relay: relay12 postfix/smtp[12811]: 8B149CB841: host ....mail.protection.outlook.com said: 451 4.7.500 Server busy. Please try again later from [...]. (S77719) [SN1NAM02FT0054.eop-nam02.prod.protection.outlook.com 2023-03-10T17:46:09.907Z 08DB2178BBEE1352] (in reply to end of DATA command) The email was not accepting the user's relay server from ServiceNow, but finally accepted it after multiple retries: Hostname=....PROD.OUTLOOK.COM 320277 bytes in 0.794, 393.629 KB/sec Queued mail for delivery) ResolutionThe instance administrator will need to check with their email administrator on local issues.Related LinksTroubleshooting inbound email messages reaching SN instance with a delay Verifying the outbound mail server received the email Enabling email delivery using SPF records to allow SN mail servers