2016 Server suddenly not sending E-mails

klsphotos
klsphotos used Ask the Experts™
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Hello Experts,

We have a web server that is suddenly not sending out e-mails.  I did not do this set up, but here is what I know:

Event IDs:

10016 Distributed Comm has been present since 5/8
2001 SMTPSVC
No usable TLS server certificate for SMTP virtual server instance '1' could be found. TLS will be disabled for this virtual-server
4006 SMTPSVC SMTP that started on 7/3



Details:

This server is a cloud server connected to our Active Directory through a IPSec VPN tunnel.  It has two network adapters, one for our internal network, one public.  Recently the hosting company looks like changed the nic settings and connection to our AD was halted because of it.  I restored it as of yesterday and Group Policy and authentication are working successfully but now these e-mails are not going out.  The developer is saying it's because of AD but I have done all checks and the server is connected successfully....so not sure if that is accurate?  

I checked IIS and SMTP and it's SMTP settings are set to go out on port 25, anonymous access, I did a DNS check under advanced delivery and it was successful,  under the outbound security tab it is set to go to our 365 support e-mail with those credentials under basic - nothing under windows authentication and TLS is checked...

Our e-mail is 365 not connected to our Active Directory.

I honestly do not see how this is a Active Directory problem and this co-worker has previously blamed network or Active directory for this set up, but I would love to be proven wrong to resolve this issue.

Please help, I have to get this working regardless of the issue and don't really understand his set up.

Thank you,

Karen
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Senior Systems Admin
Top Expert 2010
Commented:
Check the configuration settings of the receive connectors in your Office 365 to see if the one this SMTP server uses requires TLS. What would be preferable, here, would be to generate a certificate and install it in the SMTP service on your web server so it can properly encrypt messages. Failing that, having a receive connector in O365 that will accept messages that are not encrypted with TLS will resolve your issue as well.

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