I'm not buying this one, really. There's some pathos with the entity, but the rest of the elements are just… mushy.
- The extensive detail about the email protocol feels like something that people would omit entirely from other SCPs. I'm not saying it's unnecessary, it's just not very interesting.
- The containment feels like an expedient between real options. Being an uncontained phenomenon isn't a problem, I think all of mine technically are), but here… this feels like we're just getting the snapshot of a story, no beginning for the entity, no end when the Foundation contains it out. SCP narratives don't need those things, but the contents of this particular snapshot (forum post, email brouhaha) aren't particularly interesting.
- It's really hard to believe that this entity can jump into someone for a period of one or multiple days and have significant difficulty figuring out their names. I don't mean this will be easy in every situation, but in many places on Earth, people carry ID, have correspondence, or might have their email or Facebook open on the computer they have open. It can figure out email and forums, for chrissakes. It would make sense if it were cognitively different from a human at all (e.g., incapable of learning, literally can't perceive info about itself, etc.), but that's never implied. (The anomaly would probably be more interesting if it were.)
- The crosslink incident has some good emotional impact, but it doesn't make this SCP more interesting. It would be more interesting if you implied that it jumped into 2878 because/ it was interacting with the Foundation, but you didn't. It was just a random occurrence.
So, what you've got is a pretty basic idea for an entity. You've built up an emotional connection, which is good, but the mechanics of the Foundations involvement are ho-hum, and you haven't put any other twist on it.