==== REQUIRED BASIC INFO OF YOUR IREDMAIL SERVER ====
- iRedMail version (check /etc/iredmail-release): 0.98
- Linux/BSD distribution name and version: Ubuntu 18.04
- Store mail accounts in which backend (LDAP/MySQL/PGSQL): MySQL
- Web server (Apache or Nginx):Nginix
- Manage mail accounts with iRedAdmin-Pro?No
- [IMPORTANT] Related original log or error message is required if you're experiencing an issue.
====
Reverse DNS is important email server, but Azure it requires a few steps to do it. I had installed iRedMail in Azure and tried to experiment the procedures to provide rdns record. The followings are what I did and I got the rdns working:

1. In azure: Create DNS zone

Micrsoft will create 4 name servers such as ns4-08.azure-dns.com

2. assign an A record to mail.example.com (this is just an example) in the DNS zone

3. Then goto your DNS supplier. In my case I use gandi so I do: v4.gandi.com -> Modify Server

Put in the 4 Name Servers given by azure

4. Please wait for 10-20 minutes (at least) for the DNS propagation

5. Switch back to your Windows PC desktop

6. Issues these command:

7. Start the powershell in administartor mode

(now you should be in powershell mode)

a. Set-ExecutionPolicy RemoteSigned
b. Install-Module AzureRM
c. Import-Module AzureRM
d. Login-AzureRMAccount (a windows popup screen will appear, key in your credential)
e. The result will appear as:

    Name     : Azure Pass
    Id       : 8470c6de-35ae-48ef-8971-b65950343c25
    TenantId : 93cfd16f-577b-482a-bdf9-df1b3277d2cd

f. Get-AzureRMSubscription (it shows the above info)
g. Select-AzureRMSubscription -SubscriptionID 8470c6de-35ae-48ef-8971-b65950343c25
h. Get-AzureRMPublicIpAddress -ResoureGroupName yourResource -name yourVMname
i. New-AzureRMPublicIpaddress -ReverseFQDN mail.example.com -ResourceGroupName yourResource -name yourVMname -Location "southeastasia" (this is for me only) -allocationMethod Static -DomainNameLabel example

(The DomainNameLabel should be created when Azure created the vm. Goto Dashboard and look for DNS Name)

When all is done, you could check the reverse DNS is done properly through:

https://mxtoolbox.com/NetworkTools.aspx