```
Has that been tried already?
One way to solve this is to put a `Re: ` at the start of every email, but it’s a bit awkward when the first post is “re” I don’t know if a conditional "Re: " could be added…
---
### Author:  [@rumpelsepp](https://meta.discourse.org/u/rumpelsepp)
#### Post date: [April 13, 2015, 1:41pm UTC](https://meta.discourse.org/t/message-threading-in-mail-app/27521/2 "2015-04-13T13:41:23Z")
> [@watchmanmonitor](#):
>
> and I wonder.. could the / be throwing off the threading?
Does github emails thread on this client? They use the same concept of IDs.
> [@watchmanmonitor](#):
>
> I don’t know if a conditional "Re: " could be added…
from [https://meta.discourse.org/t/customize-subject-format-for-standard-emails/20801:](https://meta.discourse.org/t/customize-subject-format-for-standard-emails/20801:)
```plaintext
%{optional_re}[%{site_name}] %{optional_pm}%{optional_cat}%{topic_title}
```
---
### Author:  [@watchmanmonitor](https://meta.discourse.org/u/watchmanmonitor)
#### Post date: [April 13, 2015, 1:52pm UTC](https://meta.discourse.org/t/message-threading-in-mail-app/27521/3 "2015-04-13T13:52:27Z")
> [@rumpelsepp](#):
>
> Does github emails thread on this client? They use the same concept of IDs.
Github uses / too
Example:
> References: [discourse/discourse/issues/806@github.com](mailto:discourse/discourse/issues/806@github.com)
Thanks for pointing out the how-to topic, I’ve implemented `%{optional_re}` Nice!
---
### Author:  [@riking](https://meta.discourse.org/u/riking)
#### Post date: [April 14, 2015, 12:13am UTC](https://meta.discourse.org/t/message-threading-in-mail-app/27521/4 "2015-04-14T00:13:44Z")
> [@watchmanmonitor](#):
>
> Thanks for pointing out the how-to topic, I’ve implemented %{optional\_re} Nice!
It’s there by default… which means you removed it at some point.
---
### Author:  [@watchmanmonitor](https://meta.discourse.org/u/watchmanmonitor)
#### Post date: [April 14, 2015, 12:17am UTC](https://meta.discourse.org/t/message-threading-in-mail-app/27521/5 "2015-04-14T00:17:15Z")
I doubt I removed it.. I’ve been using Discourse for a long time and love it 💗 (Despite all my posting about desired changes.) I suspect I started the discourse forums I run before the optional re was a default, but it’s hardly worth digging up.
---
### Author:  [@codinghorror](https://meta.discourse.org/u/codinghorror)
#### Post date: [April 14, 2015, 1:27am UTC](https://meta.discourse.org/t/message-threading-in-mail-app/27521/6 "2015-04-14T01:27:03Z")
I believe you can ask @peternlewis who has [extensive experience with this](https://meta.discourse.org/t/email-notifications-not-grouping-nicely-in-mail-app/14137).
Consensus was this is a bug in mail.app with no known workaround other than the re: thing.
---
### Author:  [@peternlewis](https://meta.discourse.org/u/peternlewis)
#### Post date: [April 14, 2015, 3:50am UTC](https://meta.discourse.org/t/message-threading-in-mail-app/27521/7 "2015-04-14T03:50:09Z")
Yes, I believe @watchmanmonitor found the [relevant topic](https://meta.discourse.org/t/email-notifications-not-grouping-nicely-in-mail-app/14137/7) and adjusted the subject line config to always start with Re: which makes Mail happy, so its all good.
---
### Author:  [@rriemann](https://meta.discourse.org/u/rriemann)
#### Post date: [February 9, 2016, 12:37pm UTC](https://meta.discourse.org/t/message-threading-in-mail-app/27521/8 "2016-02-09T12:37:12Z")
The %{optional\_re} is not part of the default anymore. I have the last beta. @riking
I would have expeced that a click on reset would resolve my issue of non-threaded mails. Hower, I was already on the default. I’m using KMail from KDE and the Re is required.
---
### Author:  [@system](https://meta.discourse.org/u/system)
#### Post date: [December 17, 2018, 12:11am UTC](https://meta.discourse.org/t/message-threading-in-mail-app/27521/9 "2018-12-17T00:11:07Z")
---
### Author:  [@codinghorror](https://meta.discourse.org/u/codinghorror)
#### Post date: [December 17, 2018, 12:47am UTC](https://meta.discourse.org/t/message-threading-in-mail-app/27521/10 "2018-12-17T00:47:48Z")