wp_mail csv attachment, code review request

Hello,

I just finished coding a contactpage. Everything works fine but I’m a bit concerned that I might have overcomplicated things or wrote code that runs slow or presents a security risk.

So, for more advanced users, could you give it a quick glance and see if you see any possible problems or have some suggestions?

109 lines off code, but lots of white lines, repetitions and commenting.

[Code moderated as per the Forum Rules. Please use the pastebin]