Posts Tagged ‘Bounce back’

Recently had a customer use crazydomains for their Emails. Incoming email stopped with the error below

550 Please turn on SMTP Authentication in your mail client. []:38049 is not permitted to relay through this server without authentication.

I check the MX / NS servers to make sure they were pointing a valid records.

Called support and they asked me to remove off Automatically Detect and change to Local Mail Exchanger , it took 15 minutes to apply and starting working again. Guessing their internal DNS had an issue

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Recently a few users had the following bounce backs from Office 365 to an On-Prem Mailserver with the error

‘550 5.4.316 Message expired, connection refused(Socket error code 10061)

Checking the logs in 365 of this, this was due to the Fortigate adding some 365 SMTP servers to the IPS Quantarine List

Removing these servers from the Quarantine and also removing IPS checking in the Policy of 365 servers to on-prem via SMTP resolved this

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