My account (what I use to login) email@example.com I never use this address for sending/receiving emails and there is no real name associated with this address. I use Charlie Brown firstname.lastname@example.org in the From field (I think this is called “identity” in RB6).
When I send a message from Charlie Brown email@example.com Sent folder shows Charlie Brown (name only, no address, unchanged capitalisation).
Just for testing I sent a message from firstname.lastname@example.org which was displayed as from Charlie.Brown@Runbox.Com which IMHO is sensible, give there is no associated real name. The capitalisation in the domain part is harmless, but weird and unnecessary.
A related request: In RB6, the Sent folder displays the To: field, not From:. IMHO this is much more sensible. Please change.