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I received an e-mail with an attachment named smime.p7s (or smime.p7m). What is it?

The e-mail was signed or encrypted. But your e-mail program (e.g. webmail) does not support secure e-mail.

If it is a signed e-mail, the digital signature is displayed as a file attachment (smime.p7s). The content of the message is still visible. But you cannot verify the authenticity of the signature.

If it is an encrypted e-mail, the content is displayed as a file attachment (smime.p7m). You cannot decrypt the e-mail and view its content.