Tag Archives: SMTP

SharePoint

SharePoint 2016 SMTP Authentication

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Edit: It appears that this has been fixed in KB 3191880 :

SharePoint outbound email messages incorrectly try to authenticate to SMTP servers that support Generic Security Service Application Program Interface (GSSAPI), Kerberos, or NTLM authentication. This may prevent email messages from being sent. After you install this update, SharePoint sends email messages anonymously without authentication.

Recently I encountered an issue where SharePoint designer workflow’s emails not being delivered.

Additional inspection revealed that the messages in question were addressed to an Exchange Distribution group with “Permitted Senders.”  This designation meant that messages sent to this distribution group must be received from an authenticated sender (which SharePoint does not support by default: SHAREPOINT 2016 OUTBOUND SMTP FAILURES).

Old Solution

One solution I’ve used in the past is to setup Microsoft’s SMTP server on one of the SharePoint servers, and use that to relay (authenticated) messages to the Exchange server.   This has generally worked fine in the past, but  has always felt a little kludgey.

Seriously, Microsoft?  You’re recommending that we install IIS6 tools on a modern server?

The Problem

Anyway, the above solution breaks down with SharePoint 2016 in certain scenarios:  When sharing documents in SP2016, the “invitation” is sent as the user who initiated the invitation!!!

By default, Exchange only allows authenticated users to send as the account who’s credentials were supplied.

This presents a “Catch 22:”

  • Enable IIS6.0 SMTP relay to send Authenticated messages to Exchange and be able to relay to groups (and external domains)
    —————————-OR—————————————–
  • Configure SharePoint to send through an unauthenticated receive connector, and be allowed to send as any user, but not able to relay otuside the domain, or to groups which require authentication.

I went down a few different solution paths trying to solve this:

Failed Attempt 1: Grant Send-As Permission to SharePoint

Attempt to grant the  SharePoint SMTP service account (since I was already sending authenticated mail) “send-as” permissions on all mailboxes in the domain.

This just felt kludgey, and I was ultimately not able to get it to work.

I may have not waited the recommended 2 hours for the Mailbox Cache Idle Limit to expire:  https://technet.microsoft.com/en-us/library/aa996988(EXCHG.80).aspx

 

Successful Attempt: Configure Externally Secured Exchange Connector

The solution for me was to create a new “Externally Secured” Exchange Receive connector: https://technet.microsoft.com/en-us/library/mt668454(v=exchg.160).aspx

Essentially, this allows the hosts defined in the receive connector’s scope to deliver “unauthenticated” SMTP traffic as if it were authenticated.  

This fulfills my SharePoint requirements:

  •  To “send-as” on behalf of users in a document sharing scenario.
  • To send email as SharePoint to distribution groups which require the sender to be authenticated
  • To send email to users outside of my domain.

I hope this helps someone (even if it’s me in the future).

SharePoint

SharePoint 2016 Outbound SMTP Failures

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Recently I was configuring a SharePoint 2016 farm, and encountered some peculiar issues with outbound email.

SharePoint 2016 is the first version of SharePoint to include built-in support for TLS. In any previous version of SharePoint, TLS requirements were fulfilled by setting up a SMTP relay capable of authenticating to the desired target SMTP server.

Interestingly, It seems that SharePoint 2016 also responds to SMTP authentication challenges despite not having an explicit configuration option in Central Administration for which credentials to use for SMTP.

The issue I recently experienced is as follows:

  • List / Library “initial” alert subscription messages are delivered to the appropriate address
  • Actual alerts from a list / library are not delivered
  • Workflow Task emails are not delivered

Digging into the ULS logs of the SharePoint server, I noticed the following:

  • Messages send by w3wp (running under the web app pool service account) were delivered
  • Messages sent by OWSTIMER (running under the farm account) were not delivered.  The timer job in question is “job-immediate-alerts.”

So, despite having outbound email configured in Central Administration, it seems that SharePoint is not treating different classes of outbound email equally.

I tried many of the “well known fixes” to no avail:

  • Re-starting the server
  • Re-starting the timer service
  • Manually starting the job-immediate-alerts timer job with PowerShell
  • Altering the alerts properties of the site with stsadm

I finally broke out WireShark on my SharePoint server to observe the SMTP traffic.  What I found was interesting:

  • Messages sent by w3wp.exe had these characteristics:
    • SharePoint sends the message immediately upon request from the browser to subscribe to alerts on a library
    • SharePoint opens a SMTP session to the configured server
    • The Exchange 2013 server responds with an SMTP ntlm authentication challenge
    • The SharePoint server provides the credentials of the web app service account!
    • Exchange returns with smtp 5.7.1 client was not authenticated. 
    • SharePoint ignores the 5.7.1 error message, and delivers the message anyway
  • Message sent by OWSTIMER.exe had these characteristics:
    • SharePoint attempts to send the message with each execution of the job-immediate-alerts timer job.
    • SharePoint opens a SMTP session to the configured server
    • The Exchange 2013 server responds with an SMTP ntlm authentication challenge
    • The SharePoint server provides the credentials of the farm service account!
    • Exchange returns with smtp 5.7.1 client was not authenticated. 
    • SharePoint stops attempting to deliver the message because of the error!

In both of these scenarios, neither the farm service account, nor the web app service account are configured with Exchange mailboxes, so the authentication fails.

The receive connector in Exchange is configured to allow TLS, Exchange Authentication, and Anonymous authentication.

The unexpected behavior is this: SharePoint reacts to an SMTP 5.7.1. unauthenticated message differently depending on the context from which the SMTP session was initiated.  SMTP sessions initiated directly in the web app context succeed, but SMTP sessions initiated from timer jobs fail.

My temporary solution was to create a separate receive connector in Exchange on a separate port scoped so to only the SharePoint server’s IP that allows only anonymous authentication (it seems that by having Exchange Authentication checked, SharePoint fails).  This causes the Exchange server to never prompt the SharePoint server for STMP authentication, and therefore messages are delivered.

I’ll update this post as I discover more.