This should be doable, to an extent. We could also list the usernames directly, something like "Users X, Y, ..., and Z cannot receive emails".

Note, however, that this would only be for users that are currently shown in the participants list. If you have many participants and choose to message all without loading the full list, we would not know how many of the remaining participants can or cannot receive emails. But this might be mitigated with the choice of the text (for example, say "Users X, Y, ..., and Z and possibly others cannot receive emails").

@Daimona: Adding a sorting option to the 'Participants' tab would good.

On a separate note, do we have any existing feature requests or plans to implement a direct messaging option for users without email IDs, specifically to their talk pages on a single click. Similar to Special:MassMessage

In T397559#10984816, @Gnoeee wrote:

@Daimona: Adding a sorting option to the 'Participants' tab would good.

Sorting by what? By username or time registered should be doable, but I don't think we can add sorting by "has email". At any rate, that feature is tracked in T356912.

On a separate note, do we have any existing feature requests or plans to implement a direct messaging option for users without email IDs, specifically to their talk pages on a single click. Similar to Special:MassMessage

Yep, T321830. It was considered a few years ago but we ended up doing emails instead. I think we would like to have both eventually, but I'm not sure.

I was taking about sorting by "has email". Got it

Thank you @Daimona for sharing the tickets..