@InakViggers has great advice, but there are ways to ensure that the E-Mail was sent, stored in a back up, and not alerting the party. First thing is that if you're trying to preserve conversation by follow up e-mail, have a third party who you can BCC your email to. BCC works like an e-mail's CC, except all recipients of the e-mail in the BCC line are not known to any other recipient. So if I send an Email to Alice, and BCC Bob, Bob will see that in addition to sending him an e-mail, I sent a copy to Alice, but Alice will see that I sent an e-mail only to her. This ensures that their is a separate person receiving the record and the e-mail isn't doctored by you. Bob will not receive responses from Alice, but you can always respond to Alice with a simple "Thank you" or other follow up.
In order to ensure that the e-mail is read, attach a read receipt to every email exchange you initiate with the individual. A Read Receipt is an auto generated one time e-mail sent to you from the e-mail's receiver upon the receiver opening the email for the first time. Read Receipts do prompt the email recipient for permission to send, which they can deny, but if Alice suspects you may want to have a proof of her reading your email and that proof will hurt her, she can always deny the receipt email going to you, but then invalidates any claim Alice has to reading it when she did not (since you have to open the email to trigger the receipt, so either Alice never opened the E-Mail, which shows she was ignoring the concerns OR she did, but hid the fact, thus ignoring specifics concerns of the e-mail).