Option to mute mail about metadata-only bug changes

[Laudeci Oliveira]

For users that do a bug report, receive emails on tag's changes is useless and makes it's mail box full, so the user only have the option to stop receiving messages and receive a message when bug closes. An option to mute email on tag changes would be more appropriate.

[Данило Шеган (danilo)]

If I understand you correctly, you'd like to receive all emails except when the tags are modified? At the moment, that's not possible.

The current internal model is based on different subscription levels being subsets of one another transitively, thus it wouldn't be trivial to implement this.

[Martin Pool (mbp)]

Having just got hundreds of medium->low transition mails from lp, it
would also be nice to avoid them.

I think having a proper ordering between levels of subscription makes
sense but the current one is weird:

 * everything
 * everything except comments
 * only when closed
 * nothing

Does anyone really want mail about tag changes or priority changes but
not comments?