Do mentions still add users to an issue watch list?

[Jeramy]

We are running Jira DC 10.3. I have a user who was tagged (mentioned) on an issue. However, that user never received an e-mail from Jira. I've checked and the user does not have any rules configured in outlook, and they receive e-mails from other projects. 

We upgraded to Jira 10 recently and I'm not sure if something changed. 

The other part of this is that I added him as a watcher on a ticket, made a change where I tagged him, and he still did not receive the e-mail. However, others in the watch list did.

I'm stumped and would appreciate any help. Thank you.

[Mikael Sandberg]

One thing to check is if the user have access to the project, notifications will check permissions so if a user do not have access to the project they will not get notified even if they are mentioned/added as watchers.