allowing users to check email deliverability without creating spam
In the past year, alot of my customers have either ignored or responded very late to very important emails (many which regard presenting them an offer of a refund for a service not rendered).
So I thought now I should make a public web page where new potential customers can access a page where they can put in their email or phone number then the system sends a test message to see if they receive it before placing an order because when an order is finished, an email is sent from the same origin.
But before I go ahead, I am wondering if there are any security considerations I should be aware of.
Currently I have it where a potential customer has to enter a short random numerical code (displayed as an image) in order to run each test.
I also ensure the fields are filled in properly before submission begins.
But the part that stumps me is this....
I could add more security by allowing each email address or number to be used only one time so would-be hackers can't send the same message to the same email many times, The drawback is if I have a potential customer that is trying to make his existing email address work, he shouldn't have to make a new email address just to buy services from me.
What would you suggest I do to make the system as secure as possible without the same person receiving spam or without any potential other disasters happening? The last thing I want is for my domain to be appearing on an email blacklist.
