Q 1: Strictly, not a perl question; a mailserver &/or client question. But TBOMK, your schema implies one-addressee; one transmission, in which case, rejection (or not) as span will depend on IP from which you send (may be blocked by some agents as known open-relay, spam source or for other reasons -- and/or -- on client settings at recipient end. No absolute answer possible based on data you provide, and probably OT here.

Q 2: Suggest you start with search, super-search, google, etc. When you can refine your question within meaningful limits, we can be a lot more help.

Q 3: Answer is same as to Q 2 re searching and learning on your own effort.

Bottom Line: Please read How do I post a question effectively?