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What are PTR records and why might I need them after installing my Email Security Gateway?

Solution #00002295

Scope:
All Email Security Gateway, all firmware versions.

Answer:
Some mail domains (like aol.com) perform reverse DNS lookups to ensure the sending mail IP address matches the MX record for that domain, thereby verifying the legitimacy of the sender. Since sending and receiving IPs are often different, many hosts add PTR records to their DNS entries, linking their sending and receiving IP addresses so this type of reverse DNS lookup will not fail.

If your receiving IP address is different from your sending IP address, you will probably need to add a PTR record to your DNS records. Alternatively, you might consider using the Barracuda as an outbound relay, so your outgoing mail is actually coming from the same IP address that receives incoming mail (see Solution #00002087 for more information on setting up outbound relay).

Below is a sample PTR record for the sample IP address 1.2.3.4, retrieved using the UNIX dig utility:

$ dig -x 1.2.3.4

; <<>> DiG 9.3.1 <<>> -x 1.2.3.4
;; global options: printcmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 34627
;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 0

;; QUESTION SECTION:
;4.3.2.1.in-addr.arpa. IN PTR

;; ANSWER SECTION:
4.3.2.1.in-addr.arpa. 3600 IN PTR barracuda.domain.com.4.3.2.1
in-addr.arpa.

Link to This Page:
http://www.barracuda.com/kb?id=50160000000Gls8