Howard Miller

When you say "the session lock isn't being released", how do you know that? What is the actual symptom you are seeing?

Don't use the DB for sessions.

I'd be careful here. You can end up having different roles for all sorts of things that you don't need. It can get very confusing and hard to manage.

We dealt with this simply by changing the name of the Teacher role to "Staff". Everybody is staff. Their exact function in the course is best handled by other means - not so much by the name of a role.

Does *any* email work on your site? Or is it only a problem with Assignments?

Which Moodle version?

Has your site always done this or did it just start? If the latter, what changed? Something did.