One of the following symptoms may apply:
- Domain mail test at https://www.mail-tester.com/ or some similar resources show the following output:
CONFIG_TEXT: Testing generated the following problem:
Delivered to internal network by a host with no rDNS
This may be a false-positive, please check the reverse DNS test below to confirm or not this issue
Your reverse DNS does not match with your sending domain.
Reverse DNS lookup or reverse DNS resolution (rDNS) is the determination of a domain name that is associated with a given IP address. Some companies such as AOL will reject any message sent from a server without rDNS, so you must ensure that you have one. You cannot associate more than one domain name with a single IP address.
Your IP address 203.0.113.2 is associated with the domain 203.0.113.2.example.com. Nevertheless your message appears to be sent from vps.hostname.com. You may want to change your pointer (PTR type) DNS record and the host name of your server to the same value.
Checking the same domain on mxtoolbox.com shows:
CONFIG_TEXT: Reverse DNS does not contain the hostname
- Emails are not delivered to @hotmail.com
- The following PTR record is set for IP 203.0.113.2:
# host 203.0.113.2
18.104.22.168 in-addr.arpa domain name pointer 203.0.113.2.example.com
The following hostname is used on a server:
- Reverse DNS does not match SMTP Banner
PTR record for IP and hostname mismatch
1. Contact IP address provider (ISP) to change PTR record from 203.0.113.2.example.com to 203.0.113.2.vps.hostname.com
If PTR is specified somewhere on a name server's side, define what name server returns 203.0.113.2.example.com PTR record:
# dig +short +trace -x 203.0.113.2
77.45.in-addr.arpa. 86400 IN NS rns1.nameserver.com.
77.45.in-addr.arpa. 86400 IN NS rns2.nameserver.com.
In this case, contact nameserver.com or example.com owners.
2. Alternatively, change SMTP Banner of Mail sever: