How to check mail domain name in linux

There are a few ways to check the mail domain name in Linux:

Using the dig command:
```
dig +short mx example.com
```
Replace example.com with the domain name you want to check. This will show you the mail exchange (MX) records for the domain, which typically include the mail domain name.
Using the host command:
```
host -t mx example.com
```
This will also show you the MX records for the domain, including the mail domain name.
Using the nslookup command:
```
nslookup -type=mx example.com
```
This will also show you the MX records for the domain, including the mail domain name.
Using the getent command:
```
getent astream example.com
```
This will show you the mail domain name and other DNS records for the domain.
Using the dig +noall +answer command:
```
dig +noall +answer example.com
```
This will show you the DNS records for the domain, including the mail domain name.

Note: You may need to install the bind-utils package on your Linux system to use some of these commands.

For example, on Ubuntu-based systems:

sudo apt-get install bind9utils

On RHEL-based systems:

sudo yum install bind-utils

Once you've installed the package, you can use the commands above to check the mail domain name.