Encrypt the mail. I would recommend GnuPG, since it is strong, standard-conforming and GPLed (i.e. free).

I am not sure I agree with other respondents that suggested encryption may not be appropriate, or that you may gain something by double-encrypting through using an encrypted channel. Encryption can be made as strong as needed by the right choice of key length; if you need absolute security of the data for 10 years, I would recommend 2048 bit keys. And any issues with technical learning curve for dealing with encrypted mail for the customer should be mitigated by automatically decrypting and storing the data at the customer site. You really want to avoid spreading the security of your solution between multiple implementations/aspects, since you would have to make sure all are equally hardened.

There are multiple GPG modules available on CPAN to help you out with the implementation.

In reply to Re: [OT] E-mail security by GreyGlass
in thread [OT] E-mail security by bradcathey

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