I did a quick bit of research on this, and I wasn't really able to find anything to corroborate this. I'd be interested to know if there is a proper source to this though
Edit: there can be some concern for those metal particles, although this is no different for any metal dust by the looks of things https://forums.tomshardware.com/threads/do-old-hard-drives-contain-toxic-materials.1623183/#post-11646780
I have email addresses under Outlook (old personal account), Gmail (study provided email), Exchange (work) and Proton (main personal account). I also actively use the calendar feature in my client, which is sync'd up to my Nextcloud instance.
Just having it all under Thunderbird is so convenient and it feels more private. It's also an entirely consistent UI between accounts