Authentication
Reverse DNS (PTR record)
A DNS record that maps an IP address back to a hostname. Receiving servers check that a sending IP has a matching reverse DNS entry, and treat mail without one as suspicious.
How it works
Normal DNS turns a hostname into an IP address. Reverse DNS goes the other way: a PTR record on the IP says which hostname it belongs to. A properly configured mail server has forward-confirmed reverse DNS: the IP points to a hostname, and that hostname points back to the same IP.
Why receivers care
Compromised home computers and throwaway servers usually have generic or missing PTR records. Many mailbox providers reject or heavily filter mail from IPs without valid reverse DNS, and Gmail requires it for all senders.
Who sets it up
PTR records are controlled by whoever owns the IP address, not by your domain’s DNS. If you run your own mail server, you set it through your hosting provider. If you send through an email platform, the platform manages reverse DNS for its sending IPs.
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Full glossarySending & delivery events
MTA (Mail Transfer Agent)
The software that routes email between servers over SMTP — the underlying engine that actually delivers a message from sender to recipient.
Deliverability
Sender reputation
A score mailbox providers maintain for a sending domain or IP based on engagement, complaints and bounces, which determines whether your mail reaches the inbox, spam, or gets rejected outright.
Deliverability
Dedicated IP
A sending IP address used only by your account, giving you full control over its reputation — as opposed to a shared IP, whose reputation depends on every sender using it.