Mail not being delivered to end user

Problem reported by David Short - 7/28/2021 at 1:37 PM

Resolved

From the SMTP logs, I see that an email has hit the server, destined for an alias with about 10 people on the list. What I don't see on the bottom of the log is the delivery, which was working fine yesterday.

Anyone have any ideas as to why this would stop working? The log is below:

[2021.07.28] 15:23:42.455 [146.23.18.147][9855867] cmd: EHLO san520mox1.chevron.com
[2021.07.28] 15:23:42.487 [146.23.18.147][9855867] cmd: MAIL FROM:<DPOL@chevron.com> SIZE=20706
[2021.07.28] 15:23:42.487 [146.23.18.147][9855867] senderEmail(1): DPOL@chevron.com parsed using: <DPOL@chevron.com>
[2021.07.28] 15:23:42.487 [146.23.18.147][9855867] rsp: 250 OK <DPOL@chevron.com> Sender ok
[2021.07.28] 15:23:53.471 [146.23.18.147][43993923] cmd: EHLO san520mox1.chevron.com
[2021.07.28] 15:23:53.534 [146.23.18.147][43993923] cmd: MAIL FROM:<DPOL@chevron.com> SIZE=50162
[2021.07.28] 15:23:53.534 [146.23.18.147][43993923] senderEmail(1): DPOL@chevron.com parsed using: <DPOL@chevron.com>
[2021.07.28] 15:23:53.549 [146.23.18.147][43993923] rsp: 250 OK <DPOL@chevron.com> Sender ok

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Kyle Kerst Replied

7/28/2021 at 1:59 PM

Employee Post

Hello David! Is this the complete session from the SMTP logs? The reason I am asking is that I don't see it completing in this session. That said, if it completed SMTP you should be able to then search the Delivery logs for the sender details and find the matching local delivery. I hope that helps!

Kyle Kerst System/Network Administrator SmarterTools Inc. (877) 357-6278 www.smartertools.com

David Short Replied

7/28/2021 at 3:52 PM

Yes, this is the complete log.... I would expect to see the delivery but it is absent from the delivery log as well...

Kyle Kerst Replied

7/28/2021 at 3:56 PM

Employee Post

Thanks David. The SMTP log looks to be incomplete as it doesn't terminate, so this would prevent it reaching the delivery phase. Additionally, your original log snippet also looks like it includes more than one session.

With that being said, timeouts during SMTP usually stem from delays in our spam checks or in DNS lookups. To fix those you can try two things:

1. Within Settings>General try setting the following DNS servers at least temporarily:

1.1.1.1 (Cloudflare DNS)
8.8.8.8 (Google DNS)

2. Navigate to Settings>Antispam>RBLs/URIBLs and disable any of these lists showing a response time of 2500Ms+ for both Spool Filtering and Inbound SMTP Blocking.

When that has been implemented and saved you should then have them retry the delivery to see if it completes the SMTP session and then moves over to Delivery.

Kyle Kerst System/Network Administrator SmarterTools Inc. (877) 357-6278 www.smartertools.com

Gabriele Maoret - SERSIS Replied

7/28/2021 at 11:41 PM

Tip: check that the timeout for the SMTP IN protocol is set to at least 600 seconds (also SMTP OUT if possible).

Gabriele Maoret - Head of SysAdmins at SERSIS Currently manages 6 SmarterMail installations (1 in the cloud for SERSIS which provides services to a few hundred third-party email domains + 5 on-premise for customers who prefer to have their mail server in-house)

David Short Replied

7/29/2021 at 4:30 AM

Gabriele, thanks for your input. I have made that configuration change.

As far as the settings advised by Kyle, I have made those changes as well and I have seen additional senders in the SMTP log and not in the delivery log. Same scenario. Not sure where to go from here. It just seems that it's hitting the email server and then getting stuck somewhere.

The spool is clear and not under much load.

David Short Replied

7/29/2021 at 6:10 AM

Marked As Resolution

Well, I'm not 100% sure what it was, but it seems to have been addressed. That's the problem with shotgun fixes, you cannot be certain as to what was wrong when you have tried a bunch of things.

What I did do was double check DMARC settings and went through the spam settings. I DID add the domain as trusted and the mail started flowing about 15 minutes later.

Thanks so much for everyone's input. I will be more diligent in tracking actions next time!

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