[Users] "Thread using subject in addition to standard headers" not working?

[Thomas Leitner]

Hi,

First of all: Happy new year and thanks for making this great email
client!

I'm using the "Thread using subject in addition to standard headers"
option but it doesn't seem to work. I have set the hidden option for
the age limit to 30 days but e-mails with the same subject are still
not threaded.

The reason I would like this to work is that Jira ServiceDesk doesn't
set the headers correctly and thus all e-mails sent from it are not
threaded together.

Here are the headers from a sample ServiceDesk e-mail:

In-Reply-To: <JIRA.425202.1610015463000 at Atlassian.JIRA>
References: <JIRA.425202.1610015463000 at Atlassian.JIRA> <JIRA.425202.1610015463495 at uniwien-jirasd-1.va.smhss.de>

All e-mails from the same issue have these same In-Reply-To and
References headers. The subject is also always the same and thus should
be usable for threading. But it doesn't work.

Am I missing something here in how the option works?

Thanks for your help!

All the best,
  Thomas