I setup the exchange servers behind the firewall with the port forwarding and setup mx/dns records on ISP dns server. In order for the internal users to send email to Internet, is a PTR record created on ISP dns server mandatory? Why? Thanks.

Not mandatory just best practice. The reverse record says that your IP resolves to the mx record of your domain. Some orgs may block you if you don't have a reverse record.James Chong MCITP | EA | EMA; MCSE | M+, S+ Security+, Project+, ITIL msexchangetips.blogspot.com

Every host should have a valid PTR record in DNS regardless. That being said, you absolutely should have a reverse record for each SMTP gateway that sends mail to the internet that can be resolved by recipient servers or you will have a lot of problems delivering mail. The PTR in this case is for the ip address of the sending servers which may or may not be the same servers that receive mail.

Yes, As stated by Andy and James, if you do not ask your ISP to set up a PTR, many spam filters will not let your mail through. It's a necessity for good e-mail communications.Chazzie / IT Manager Advanced Door Controls, Inc.

Thanks everyone. SFP record is different from PTR record on Anti-spam, is it? Can you explain how they work differently? Thanks.

We had an issue with this when we move to another ISP. You need to tell your provider to explicitly create a reverse DNS record for you.

Thanks everyone. SFP record is different from PTR record on Anti-spam, is it? Can you explain how they work differently? Thanks. SPF: http://www.openspf.org/ And yes, you should publish a SPF record in DNS as well. It tells recipient's SMTP gateways which sending server ips are allowed to send as your SMTP domains. ( And you should implement your own SPF checking as well!)

Hi Ian3, Yes, SPF record is different from PTR record. The PTR record is just as Andy said. If the PTR record for the source domain does not exist or is incorrect. The destination SMTP server will not deliver the message. SPF Record is used to specify which hosts are allowed to send e-mail from a given domain in the public Domain Name System(DNS). Thanks, Evan Please remember to click “Mark as Answer” on the post that helps you, and to click “Unmark as Answer” if a marked post does not actually answer your question. This can be beneficial to other community members reading the thread.