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What is an smime.p7s file attachment and how do I open it?

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There’s no need to open the s/mime.p7s attachment, it’s just a digital signature

Trying to open an smime.p7s email attachment that looks like this?
smime p7s file

Email and Document Signing Certificates are a fantastic product that haven’t managed to become ubiquitous yet owing to the fact that they are still unsupported by many mail clients. That lack of universal support has led to one of the most common questions people have about their email: what is an smime.p7s file? And how do I open it?

S/MIME stands for Secure/Multipurpose Internet Mail Extensions, the SMIME.p7s file format is the digital signature that is sent alongside a digitally signed email. If you’re receiving emails with an SMIME.ps7 attachment in the email, it means that the sender has an Email Signing certificate installed on their computer. If your email client supports Email Signing you will see the verified name of the sender. Microsoft Outlook represents this with a little ribbon, for example, like this:
smime email signing ribbon

When you click on the ribbon or whatever Icon accompanies the verified sender field, you will be greeted with validated information on the sender, including who issued the Email signing certificate in the first place:
digital signature valid

How do I get my own digital signature for my emails?

With a digital signature, you can sign and/or encrypt the emails you send to others. You can easily purchase and install your own digital certificate in Microsoft Outlook or other email program to sign and encrypt messages.

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Can I open an SMIME.p7s file?

Technically you can open a p7s file in Microsoft Outlook, but it’s not really a file that’s necessarily meant for a user to open, it’s their for the email client to authenticate the sender of the secure email message. There’s not really much you get out of opening it.

Do I need email signing?

Email & Document Signing Certificates are called CPACs (Comodo Personal Authentication Certificates) and can be used to sign both emails and certain kinds of documents. Signing accomplishes several things:

  • First of all, it verifies the identity of the sender so that you know the message is authentic.
  • It also flags you if the email or document have been tampered with and can restrict access.
  • Optionally, you can encrypt the email so only the intended recipient can read it.

These are all great things, especially for larger companies and organizations.

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What is S/MIME? How does it work? Do I need S/MIME?