I have encountered exceptions in the Microsoft.AspNetCore.Server.Kestrel module with SM on Linux (latest version on Debian 13 fully updated).

Problem reported by Gabriele Maoret - SERSIS - 8/3/2026 at 7:47 AM

Resolved

I see these errors (in red in the image):

Does anyone know what these might be?

NOTE: SmarterMail still appears to be working properly...

I'll add more details here:

ago 03 16:38:52 sm-DOMAIN MailService[841]: Microsoft.AspNetCore.Server.Kestrel[0] Unhandled exception while processing 0HNNHDIKERHAP. System.NullReferenceException: Object reference not set to an instance of an object. at Microsoft.AspNetCore.Server.Kestrel.Https.Internal.HttpsConnectionMiddleware.ServerOptionsCallback(SslStream sslStream, SslClientHelloInfo clientHelloInfo, Object state, CancellationToken cancellationToken) at System.Net.Security.SslStream.ReceiveHandshakeFrameAsync[TIOAdapter](CancellationToken cancellationToken) at System.Net.Security.SslStream.ForceAuthenticationAsync[TIOAdapter](Boolean receiveFirst, Byte[] reAuthenticationData, CancellationToken cancellationToken) at Microsoft.AspNetCore.Server.Kestrel.Https.Internal.HttpsConnectionMiddleware.OnConnectionAsync(ConnectionContext context) at Microsoft.AspNetCore.Server.Kestrel.Core.Internal.Infrastructure.KestrelConnection`1.ExecuteAsync()

ago 03 16:38:53 sm-DOMAIN MailService[841]: Microsoft.AspNetCore.Server.Kestrel[0] Unhandled exception while processing 0HNNHDIKERHAR. System.NullReferenceException: Object reference not set to an instance of an object. at Microsoft.AspNetCore.Server.Kestrel.Https.Internal.HttpsConnectionMiddleware.ServerOptionsCallback(SslStream sslStream, SslClientHelloInfo clientHelloInfo, Object state, CancellationToken cancellationToken) at System.Net.Security.SslStream.ReceiveHandshakeFrameAsync[TIOAdapter](CancellationToken cancellationToken) at System.Net.Security.SslStream.ForceAuthenticationAsync[TIOAdapter](Boolean receiveFirst, Byte[] reAuthenticationData, CancellationToken cancellationToken) at Microsoft.AspNetCore.Server.Kestrel.Https.Internal.HttpsConnectionMiddleware.OnConnectionAsync(ConnectionContext context) at Microsoft.AspNetCore.Server.Kestrel.Core.Internal.Infrastructure.KestrelConnection`1.ExecuteAsync()

Gabriele Maoret - Head of SysAdmins and CISO at SERSIS

Currently manages 7 SmarterMail installations (1 in the cloud for SERSIS which provides services to a few hundred third-party email domains + 6 on-premise for customers who prefer to have their mail server in-house)

2 Replies

Reply to Thread

Tony Scholz Replied

8/3/2026 at 11:00 AM

Employee Post Marked As Resolution

Hello,

Messages that begin with the following can generally be ignored in this scenario.

Microsoft.AspNetCore.Server.Kestrel[0] Unhandled exception while processing 0HNNHDIKERHAP.

These messages are generated while SNI certificates are being processed and no fallback certificate is found. This can show up in your logs frequently if your server gets probed often.

Thank you

Tony Scholz

Lead Network/System Administrator

SmarterTools Inc.

www.smartertools.com

Gabriele Maoret - SERSIS Replied

8/3/2026 at 11:06 AM

Ok, thaks Tonyn

Gabriele Maoret - Head of SysAdmins and CISO at SERSIS

Back to Community Threads

Reply to Thread

Enter the verification text