Azure VMs can indeed host email servers, but with important caveats. The core technical constraints you'll face are:

• Azure's reverse DNS limitations (PTR records)
• Dynamic IP reputation issues
• Port 25 blocking in some regions

Azure now allows assigning static public IPs, but reverse DNS remains problematic. Here's a practical solution:

# Example PowerShell to assign static IP
New-AzPublicIpAddress -Name "EmailServerIP" -ResourceGroupName "EmailResources" 
-AllocationMethod Static -Location "EastUS" -DomainNameLabel "yourdomain"

For outgoing emails, configure SPF, DKIM and DMARC records to compensate:

# Sample SPF record (DNS TXT)
"v=spf1 ip4:YOUR.AZURE.IP.ADDRESS include:spf.protection.outlook.com -all"

# Sample Postfix configuration for DKIM
smtpd_milters = inet:localhost:8891
non_smtpd_milters = inet:localhost:8891
milter_default_action = accept

Azure blocks port 25 by default on new subscriptions. Request unblocking via:

1. Azure Portal > Support > New support request
2. Select "Service and subscription limits"
3. Request "SMTP Port 25 Unblock"

Alternative architecture using port 587:

# Postfix master.cf configuration
submission inet n - n - - smtpd
  -o syslog_name=postfix/submission
  -o smtpd_tls_security_level=encrypt
  -o smtpd_sasl_auth_enable=yes

For your polling-based requirement, consider these lightweight solutions:

Here's a minimal Docker-compose setup for Mailu:

version: '3'

services:
  server:
    image: mailu/nginx:$VERSION
    ports:
      - "25:25"
      - "587:587"
    volumes:
      - "/mailu/certs:/certs"
    environment:
      - DOMAIN=yourdomain.com
      - HOSTNAMES=mail.yourdomain.com
      - TLS_FLAVOR=cert

Essential checks to prevent spam listing:

# Check IP reputation
curl https://www.spamhaus.org/query/ip/YOUR_IP
# Verify DNS records
dig TXT yourdomain.com
dig MX yourdomain.com

For automated monitoring, implement this Python script:

import dns.resolver
import smtplib

def check_mx_records(domain):
    try:
        mx_records = dns.resolver.resolve(domain, 'MX')
        return [str(r.exchange) for r in mx_records]
    except:
        return False

def test_smtp_connection(host):
    try:
        with smtplib.SMTP(host, 25, timeout=10) as smtp:
            return smtp.noop()[0] == 250
    except:
        return False

Running a basic email server on Azure Virtual Machines is technically possible using open-source solutions like Postfix+Dovecot or Microsoft Exchange. The core challenge isn't virtualization itself, but Azure's networking constraints affecting email deliverability. Key observations from production deployments:

# Sample Postfix main.cf configuration for Azure
myhostname = mail.yourdomain.com
mydomain = yourdomain.com
myorigin = $mydomain
inet_interfaces = all
mydestination = $myhostname, localhost.$mydomain, localhost, $mydomain
relayhost = 
mynetworks = 127.0.0.0/8 [::ffff:127.0.0.0]/104 [::1]/128
smtpd_banner = $myhostname ESMTP

Azure's primary limitation for email servers is the lack of customizable rDNS (PTR records) for VM public IPs. Microsoft only provides reverse DNS resolution to *.cloudapp.azure.com addresses, which triggers spam filters when sending mail.

Workaround options:

• Azure's Outbound SMTP Relay (requires Azure subscription whitelisting)
• SMTP relay services (SendGrid, Mailgun) for outgoing mail only
• Using Azure App Service Hybrid Connections

For your specific use case of primarily receiving emails with occasional responses, consider this hybrid approach:

# Python email polling example using IMAP
import imaplib
import email

def poll_emails():
    mail = imaplib.IMAP4_SSL('your-azure-vm-ip')
    mail.login('user@domain.com', 'password')
    mail.select('inbox')
    
    typ, data = mail.search(None, 'UNSEEN')
    for num in data[0].split():
        typ, msg_data = mail.fetch(num, '(RFC822)')
        raw_email = msg_data[0][1]
        email_message = email.message_from_bytes(raw_email)
        process_email(email_message) # Your custom logic
        
    mail.close()
    mail.logout()

To maximize inbox placement when sending occasional responses:

1. Configure SPF records with Azure's outbound IP ranges
2. Implement DKIM signing on your VM
3. Set up DMARC policies for monitoring
4. Warm up IP reputation with low initial volumes

If deliverability becomes critical, consider these Azure-native patterns:

// C# example using Azure Functions + Storage Queues
[FunctionName("ProcessEmail")]
public static async Task Run(
    [QueueTrigger("incoming-emails")] string queueItem,
    [Table("EmailLogs")] IAsyncCollector tableBinding,
    ILogger log)
{
    var email = JsonConvert.DeserializeObject(queueItem);
    await tableBinding.AddAsync(new EmailEntity {
        PartitionKey = DateTime.UtcNow.ToString("yyyyMMdd"),
        RowKey = Guid.NewGuid().ToString(),
        Subject = email.Subject,
        Processed = false
    });
    
    // Additional processing logic
}