You should send a test statement. The customer can open it and click a link, as an example, that takes them to your site and you then verify that they can receive, open and follow directions on it. YOu could also have a name and number in it for them to call and verify with.
Short of having them open an encrypted file, you only proved otherwise that the mail didn't bounce back at you.
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AndyZ CRCM
My opinions are not necessarily my employers.
R+R-R=R+R
Rules and Regs minus Relationships equals Resentment and Rebellion. John Maxwell