PTR 记录是否由常见的网络托管服务使用，例如：smtp、pop、imap、dns 解析、http、https、ftp、ssl 和 tls？
答案1
从维基百科页面：
The most common uses of the reverse DNS include:
- The original use of the rDNS: network troubleshooting via tools such as
traceroute, ping, and the "Received:" trace header field for SMTP e-mail,
web sites tracking users (especially on Internet forums), etc.
- One e-mail anti-spam technique: checking the domain names in the rDNS to
see if they are likely from dialup users, or dynamically assigned
addresses unlikely to be used by legitimate mail servers. Owners of such
IP addresses typically assign them generic rDNS names such as
"1-2-3-4-dynamic-ip.example.com." Some anti-spam filters assume that
email that originates from such addresses is likely to be spam, and may
refuse connection.
- A forward-confirmed reverse DNS (FCrDNS) verification can create a form
of authentication showing a valid relationship between the owner of a
domain name and the owner of the server that has been given an IP
address. While not very thorough, this validation is strong enough to
often be used for whitelisting purposes, mainly because spammers and
phishers usually can't pass verification for it when they use zombie
computers to forge domains.
- System logging or monitoring tools often receive entries with the
relevant devices specified only by IP addresses. To provide more
human-usable data, these programs often perform a reverse lookup before
writing the log, thus writing a name rather than the IP address.
答案2
查找 PTR 记录的常见用途是垃圾邮件过滤器。这个想法背后的概念是，使用虚假域名发送电子邮件的垃圾邮件发送者通常不会在 ISP DNS 区域设置适当的反向 PTR。垃圾邮件过滤器使用此标准来检测垃圾邮件。如果您的域没有适当的反向 PTR 记录设置，那么大多数电子邮件垃圾邮件过滤软件很可能会阻止来自您的邮件服务器的电子邮件。