It should be taken into account that some e-mail applications check whether the electronic address from where the mail was sent is included in the certificate used to sign the messages, for online services based on signed e-mails. If it is not included, the messages can not be signed.
Therefore, to avoid possible problems, if the certificate is to be used for sending a secure e-mail, we recommend including the electronic address from which the messages are going to be sent. If the user already has a certificate without an e-mail address, he/she is recommended to obtain a new one that includes it.