Email can also send information by encrypted attachments. The file is encrypted using software on the sender’s device and added as an attachment to a standard email.
In order to decrypt the attachment the recipient must have compatible software (in some cases the same software) and have access to the key. Commonly the key is derived from a shorter, more-memorable password which can be transferred to the recipient; however the password must be sufficiently long and complex to prevent compromise.
To achieve the maximum guarantees that can be offered by the use of encrypted attachments the key must be communicated over a separate communication channel, eg by disclosing the password over the telephone upon confirmation that the email has been delivered. Including the password within the same email as the encrypted attachment affords little protection to the encrypted personal data.
A common limitation to this method of data transfer is that most email providers will set an upper limit on the size of attachments that can be sent and received. Encrypted attachments that exceed any such limit would not be successfully sent.