Merge pull request #52324 from davegoddard/patch-3

Added a note about SMTP support

Author: ktoliver

articles/firewall/overview.md

@@ -111,7 +111,7 @@ Network filtering rules for non-TCP/UDP protocols (for example ICMP) don't work
 |Availability zones can only be configured during deployment.|Availability zones can only be configured during deployment. You can't configure Availability Zones after a firewall has been deployed.|This is by design.|
 |SNAT on inbound connections|In addition to DNAT, connections via the firewall public IP address (inbound) are SNATed to one of the firewall private IPs. This requirement today (also for Active/Active NVAs) to ensure symmetric routing.|To preserve the original source for HTTP/S, consider using [XFF](https://en.wikipedia.org/wiki/X-Forwarded-For) headers. For example, use a service such as [Azure Front Door](../frontdoor/front-door-http-headers-protocol.md#front-door-to-backend) or [Azure Application Gateway](../application-gateway/rewrite-http-headers.md) in front of the firewall. You can also add WAF as part of Azure Front Door and chain to the firewall.
 |SQL FQDN filtering support only in proxy mode (port 1433)|For Azure SQL Database, Azure SQL Data Warehouse, and Azure SQL Managed Instance:<br><br>During the preview, SQL FQDN filtering is supported in proxy-mode only (port 1433).<br><br>For Azure SQL IaaS:<br><br>If you're using non-standard ports, you can specify those ports in the application rules.|For SQL in redirect mode (the default if connecting from within Azure), you can instead filter access using the SQL service tag as part of Azure Firewall network rules.
-|Outbound traffic on TCP port 25 isn't allowed| Outbound SMTP connections that use TCP port 25 are blocked. Port 25 is primarily used for unauthenticated email delivery. This is the default platform behavior for virtual machines. For more information, see more [Troubleshoot outbound SMTP connectivity issues in Azure](../virtual-network/troubleshoot-outbound-smtp-connectivity.md). However, unlike virtual machines, it isn't currently possible to enable this functionality on Azure Firewall.|Follow the recommended method to send email as documented in the SMTP troubleshooting article. Or, exclude the virtual machine that needs outbound SMTP access from your default route to the firewall. Instead, configure outbound access directly to the Internet.
+|Outbound traffic on TCP port 25 isn't allowed| Outbound SMTP connections that use TCP port 25 are blocked. Port 25 is primarily used for unauthenticated email delivery. This is the default platform behavior for virtual machines. For more information, see more [Troubleshoot outbound SMTP connectivity issues in Azure](../virtual-network/troubleshoot-outbound-smtp-connectivity.md). However, unlike virtual machines, it isn't currently possible to enable this functionality on Azure Firewall. Note: to allow authenticated SMTP (port 587) or SMTP over a port other than 25, please make sure you configure a network rule and not an application rule as SMTP inspection is not supported at this time.|Follow the recommended method to send email, as documented in the SMTP troubleshooting article. Or, exclude the virtual machine that needs outbound SMTP access from your default route to the firewall. Instead, configure outbound access directly to the internet.
 |Active FTP isn't supported|Active FTP is disabled on Azure Firewall to protect against FTP bounce attacks using the FTP PORT command.|You can use Passive FTP instead. You must still explicitly open TCP ports 20 and 21 on the firewall.
 |SNAT port utilization metric shows 0%|The Azure Firewall SNAT port utilization metric may show 0% usage even when SNAT ports are used. In this case, using the metric as part of the firewall health metric provides an incorrect result.|This issue has been fixed and rollout to production is targeted for May 2020. In some cases, firewall redeployment resolves the issue, but it's not consistent. As an intermediate workaround, only use the firewall health state to look for *status=degraded*, not for *status=unhealthy*. Port exhaustion will show as *degraded*. *Not healthy* is reserved for future use when the are more metrics to impact the firewall health.
 |DNAT isn't supported with Forced Tunneling enabled|Firewalls deployed with Forced Tunneling enabled can't support inbound access from the Internet because of asymmetric routing.|This is by design because of asymmetric routing. The return path for inbound connections goes via the on-premises firewall, which hasn't seen the connection established.