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550 no rDNS entry

‘550 No rDNS entry for x.y.z.n’ explained and resolved

‘550 no rDNS entry for’ means that there is no reverse DNS record for the sending email server.

You may see this error in logs :

Tue 2018-09-04 10:36:46: <-- 550-Sending server has no reverse DNS (PTR record)

Or you may get a bounce back message :>: host mail.[destination_ip] said: 550 No rDNS entry for 100.200.300.400 (in reply to RCPT TO command)