Follow the gmail community thread here: https://support.google.com/mail/thread/14607605?hl=en

@TommyLike could you please let us know does this issue only occur on gmail system? and what kind of PTR do you suggest? thanks

/assign @TommyLike

this issue is assigned to: @TommyLike.

Hi， I am expert with SMTP protocol.
A PTR record is a kind of DNS record that reverse point an IP to a domain. You should ask IP addr provider(ISP like 电信) to add the PTR for you. For example:

DNS A record: mail.openeuler.org -> 1.1.1.1
DNS PTR record: 1.1.1.1 -> mail.openeuler.org. (when setup record, it's not 1.1.1.1 by the way).

With this PTR record, email receiver system(gmail) knows that the sender owns the IP. (by checking whether email sender(domain) and email send IP matches, otherwise someone may send fake emails).

This is a kind of spam email protection mechanism.

By the way, you should setup TXT record like "v=spf xxxxx" too，almost all email system will check this record.

@freesky-edward @TommyLike

@Qianbiao.NG thanks, from what I know, we already have configured as what you are saying. @freesky-edward have more detail to share, but we are very gladed that you can help us with our mail system, since there are still some features and issues left here, for example the Unicode issue。

yeah, we already support the PTR,spf,dmarc,dkim currently. please refer to [dns definition] (https://gitee.com/openeuler/infrastructure/blob/master/environment/huaweicloud/resources.tf#L124) for more detailed information.
@Qianbiao.NG thank you so much anyway.
@TommyLike is it time to close this isuss now?

ok, NP.