A magic word might be the way to go here.

https://www.mediawiki.org/wiki/Help:Magic_words#Page_names

Something like {{PAGENAMEBEFOREREDIRECT}} that can then be inserted into the MassMessage as "Hello {{PAGENAMEBEFOREREDIRECT}}" or "(This message is intended for {{PAGENAMEBEFOREREDIRECT}}"

We should carefully examine the existing magic word list and see if any of the existing ones would work. If not, we can consider creating a new one.

Another option is a message could be automatically prepended in the case of a redirect. "(This message was sent to User talk:ABC and is being posted here due to a redirect.)"

Change #1148607 had a related patch set uploaded (by Novem Linguae; author: Novem Linguae):

[mediawiki/extensions/MassMessage@master] notify message recipients when a redirect was followed

https://gerrit.wikimedia.org/r/1148607

In T394413#10831691, @Novem_Linguae wrote:

Another option is a message could be automatically prepended in the case of a redirect. "(This message was sent to User talk:ABC and is being posted here due to a redirect.)"

I fear this can mess up the message layout, especially if it’s appended unconditionally (i.e. the message sender cannot opt out of it). For example, if it comes after the signature, DiscussionTools will not recognize it as part of the message. What about including it in the edit summary? Wouldn’t that be visible enough? (It probably wouldn’t work with Flow and LiquidThreads, but those are deprecated anyway, so I wouldn’t care about them too much. Normal editing allows specifying different topic titles and edit summaries.)

Change #1148607 merged by jenkins-bot:

[mediawiki/extensions/MassMessage@master] notify message recipients when a redirect was followed

https://gerrit.wikimedia.org/r/1148607

In T394413#10974411, @Tacsipacsi wrote:

In T394413#10831691, @Novem_Linguae wrote:

Another option is a message could be automatically prepended in the case of a redirect. "(This message was sent to User talk:ABC and is being posted here due to a redirect.)"

I fear this can mess up the message layout, especially if it’s appended unconditionally (i.e. the message sender cannot opt out of it). For example, if it comes after the signature, DiscussionTools will not recognize it as part of the message. What about including it in the edit summary? Wouldn’t that be visible enough? (It probably wouldn’t work with Flow and LiquidThreads, but those are deprecated anyway, so I wouldn’t care about them too much. Normal editing allows specifying different topic titles and edit summaries.)

Apologies, I meant to respond to this then got busy.

I do lean towards the message being in the wikitext rather than in an edit summary. There's no guarantee that the person will read the edit summary. Also, bot edits are sometimes hidden from watchlists. I'm not 100% sure if this applies to MediaWiki Message Delivery, but if it did, then an edit summary would be very low visibility.

I guess I could have been prepended to the message (between the heading and the body text) instead of appended to the message to solve the DiscussionTools [reply] button issue. If there's any kind of complaints about this patch, maybe we can do a follow up patch that changes it to prepend.

I don't think these potential problems are significant. You wouldn't often reply to mass-message comments anyway. And I definitely agree with putting the notice in the content rather than the summary, no one reads summaries on talk pages (and no one should).

@Novem_Linguae I believe this feature leads to unexpected redirect notifications due to https://www.mediawiki.org/wiki/Extension:MassMessage#Configuration_parameters -> $wgNamespacesToConvert = [ NS_USER => NS_USER_TALK ];
Many mass message lists just include the user name instead of directly linking to the user talk page. I just send a test message to myself -> https://test.wikipedia.org/wiki/User_talk:Johannes_Richter_(WMDE) which automatically got the following text attached: (This message was sent to User:Johannes Richter (WMDE) and is being posted here due to a redirect.)

In T394413#11193613, @Johannes_Richter_WMDE wrote:

@Novem_Linguae I believe this feature leads to unexpected redirect notifications due to https://www.mediawiki.org/wiki/Extension:MassMessage#Configuration_parameters -> $wgNamespacesToConvert = [ NS_USER => NS_USER_TALK ];
Many mass message lists just include the user name instead of directly linking to the user talk page. I just send a test message to myself -> https://test.wikipedia.org/wiki/User_talk:Johannes_Richter_(WMDE) which automatically got the following text attached: (This message was sent to User:Johannes Richter (WMDE) and is being posted here due to a redirect.)

Did some further testing: * {{target |page =User:Johannes Richter (WMDE) |site=test.wikipedia.org}} leads to the redirect notification, * {{target |user =Johannes Richter (WMDE) |site=test2.wikipedia.org}} didn't, so it's probably just something mass message senders should know if they want to avoid the notification.