You might get a regex via the filtaquilla addon. It adds a lot of powerful options to filters, including Regex on subjects and header and javascript actions. It is like many advanced tools assuming you know what you are doing with a regex and javascript. https://addons.thunderbird.net/en-US/thunderbird/addon/filtaquilla/

Ok, so in filterquilla does "property doesn't contain this regex" mean it'll match when the header property isn't present at all?

I have no idea. I did not write the thing, nor do I actually claim to know what a regex is or does. If it was me I would just test it on a small collection of email to determine what is does.

Did you consult the documentation? https://quickfilters.quickfolders.org/filtaquilla.html Have a look at the open issues? https://github.com/RealRaven2000/FiltaQuilla/issues Use the support email in the link I provided? [email protected]

Alternatively you could simply check for the existence of the five possible values of the header rather than the simple presence of the header. Probably my preferred choice as it has so few possible values although a criteria specifying the header being not equal to " " may be enough or begins with is not "Z" would also work as none of the valid values begins with a Z. https://docs.gitlab.com/ee/user/profile/notifications.html#x-gitlab-notificationreason

X-GitLab-NotificationReason The X-GitLab-NotificationReason header contains the reason for the notification. The value is one of the following, in order of priority: own_activity assigned review_requested mentioned subscribed The reason for the notification is also included in the footer of the notification email. For example, an email with the reason assigned has this sentence in the footer:

> nor do I actually claim to know what a regex is or does

See https://en.wikipedia.org/wiki/Regular_expression#POSIX_basic_and_extended

Anyway, filterquilla has turned out to be too slow, probably because regexes can be quite slow to run. I've ended up using two filters, one to filter by project and apply a tag for "peer review" and the specific project, and then another filter to move messages that have "peer review" but don't mention me.