If what your system calls “junk” is what mine calls “Spam”, I do have some legitimate messages go there.
Fortunately BTInternet does tell you there are messges in “Spam”, so I can act promptly.
(There is a “safe senders” list but you don’t need use it, which is as well because I’m blowed if I can find it. I did once, but not since.)
I don’t seem to receive what may be genuine but cold-call sales e-posts. Those usually arrive as land-line ‘phone calls. Asking the caller firmly things like, “Which survey and how did my home enter it?” (for loft insulation in that case) frightens them off. The seller might be real but his survey claim bogus, made in hope.