Alarming unknown email address auto-suggestions in IOS mail

Not sure if this is the right area but I do not know where else to post. I recently started using ios Mail and when I type the first letters, it auto-suggests email addresses. We just switched over from Android to Iphones/Ipads.. I was surprised to find a number of unknown e-mail address it auto-suggested and I'm 100% sure I have never communicated to these people in the past.

Looking deeper, I googled each e-mail address (a few had the first, last name patterns) and found out these are people living near me. One of them is my next door neighbor and neither me , nor my wife knows her e-mail address. A few others within a 5 - house proximity. The only person familiar to us is the next door neighbor and the rest, shows up in Google as folks near me.

I do not know where the auto-suggestions are coming from and I can only tell you what I suspect. Maybe someone here can help:

1) I turned on find my Iphone (for myself and family)

2) I turned on Find Friends (family only)

3) I have Airdrop on but only to contacts

4) We use Comcast Xfinitiy and I know about the Xfinity Home Hotspot where it allows strangers with an Xfinity account to use my wifi as a hotspot

5) We also use Tmobile's personal WIFI - Cellspot

6) Location Service is set to on

7) The auto-suggestion emails offered are not in any of my contacts list

I suspect it has something to do with geo location/fencing and wifi access point mapping done by many companies.

My questions are:

1) Where are these email addresses coming from? (from a technology standpoint)

2) How do I prevent this? For my family's and neighbor's privacy.

3) Why would mail auto-suggest emails not coming from my contacts?

BTW - the same contacts are auto-suggested in my wife's phone as well. She also do not the have the email addresses as contacts nor does she know them except for our next door neighbor.

Thanks Matt