TFS 2017 - Duplicate Email notifications - tfs

Question

Using TFS 2017 Update 2, we notice that we sometimes get some email notification double, with a lot of time (30 minutes) between them.
We are not using distributions lists, users are added to TFS Teams directly.
When checking the View link in the bottom, its shows the same ID for all duplicate emails, so its the same alert triggering it.
A concrete example
Build completed at 11:18 AM. We received an identical notification at 11:37, 11:53 and 12:09.
First issue is already that there is 20 minutes between the completion of the build and the sent of the first message.
What part of TFS should i troubleshoot here, we have noticed before that email alerts are received later then expected.
So we have 2 issues, which might be related
1. Emails arrive up to 30 minutes later than expected
2. Identical Emails sometimes are received 2/3 times.
Update, issue came back.
Technical Details:
Build Ran for 15.3 minutes (Default), completed at Fri 12/01/2017 01:48 PM
1st email header:
Received: from TFSAPPSERVER (ip) by smtphost.domain.com
(ip address) with Microsoft SMTP Server id 14.3.319.2; Fri, 1 Dec 2017
07:50:34 -0600 ( 01:50 PM tranlated to same time above)
2nd email header:
Received: from TFSAPPSERVER (ip) by smtphost.domain.com
(ip address) with Microsoft SMTP Server id 14.3.319.2; Fri, 1 Dec 2017
08:26:37 -0600 ( 02:26 PM tranlated to same time above)

Answer 1

In this thread there is a solution from Microsoft:
The root of our issue was that the SMTP server was not responding to TFS to indicate that the mail was sent within the timeout period. Thus the fix in our case was simply to increase the timeout that TFS waits before re-sending emails.
To do this, we ran the following in the TFS Configuration database to change the timeout from 10 seconds (the default) to 90 seconds:
exec prc_SetRegistryValue 1, '#\Service\Integration\Settings\SendTimeout\', 90000