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Exchange 2016 email stuck in Submission queue

Two days ago, I began using SpamTitan Cloud for my spam filtering.  I am running a trial (30 day).  Because of that, my outbound email is still going through the old spam service (ST does not support outbound until after the trial).  Everything seemed fine until this morning.  Email is reaching my Exchange 2016 server but is not progressing beyond the Submission queue.  Outbound email is also being held up in this queue.

The queue is showing errors such as "Message deferred by categorizer agent" and "[{LED=400 4.4.7 Message delayed}...].

Is the problem related to my config with SpamTitan or is it something internal?  Waht should I be looking at.  I have tried reboots and stop/starting MSExch Transport.

Exchange* spam filter

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8/22/2022 - Mon
Lee W, MVP

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Lee W, MVP

It's a quick fix (workaround) - see the blog link I posted.  Then keep an eye out for an official MS patch.

You're solution worked perfectly.  The only question I have is - why did it suddenly stop working today?
Lee W, MVP

It's basically a Y2K problem.

Some genius at Microsoft decided to convert dates into a 10 digit number YYMMDD and I'd assume the last 4 digits represent either HHMM or the percentage of the day that has passed.

Then they instructed the code to use a signed Long Integer value to store that number.  Signed long integers have a maximum value of 2147483647.  So on December 31, 2021, the value would have been 211231xxxx - less than 2147483647.  But when the clock rolled over to January 1, 2022, 220101xxx > 2147483647 which killed the anti-malware service and that triggered the Transport service to stop relaying mail to the mailboxes.  By disabling the antimalware service, it's no longer an issue.  Of course, you may be at a greater risk of having malware get into your mailboxes, but it's either that or stop getting email...

Microsoft has since provided instructions for correcting this issue. Email Stuck in Transport Queues - Microsoft Tech Community
Experts Exchange has (a) saved my job multiple times, (b) saved me hours, days, and even weeks of work, and often (c) makes me look like a superhero! This place is MAGIC!
Walt Forbes

Doh!  Thanks for the post-mortem.

You would think they would have learned...