Eden Allen
Eden's Blog on Cyber Security Awarness


Eden's Blog on Cyber Security Awarness


SMIME.p7s – What Is It & How to Open It?

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Eden Allen
·Dec 9, 2022·

5 min read


Know All About A Smime.p7s File That’s Often Seen In An Email Attachment

Have you ever received an email that contains smime.p7s file attachment? If yes, you might have many questions about what it means, if it is safe, and whether or not you should open it. So if you see this file attachment in your email, do not panic. It is used to confirm the sender’s identity and facilitates the exchange of encrypted emails. It is nothing to worry about and is not something you can open.

Document signing and email certificates happen to be amazing products. However, it is not ubiquitous due to the fact that many mail clients do not support mail clients. The lack of universal support has resulted in the most common questions people have about that email: what is an smime.p7s file, and how do I open it? So let us find what it is.

What is the Smime p7s File?

S/MIME stands for Secure/Multipurpose Internet Mail Extension, and the Smime p7s file format is the digital signature the sender sends with a digitally signed email. So when a person receives an email with this file attachment, it means that the sender possesses an email signing certificate installed on their system. If your email client supports email to sign in, you will always see the verified name of the sender.

Secure/ Multipurpose Internet Mail Extensions are one of the IETF standards that the users use for signing mime data and public key encryption. It provides various cryptographic security functionalities such as data encryption, authentication, the privacy of email applications, message integrity, and non-repudiation of origin.

Having said that, before anyone can use it in their email application, they must obtain an email and document signing certificate from a publicly recognised CA. Once the users buy and install an email signing certificate file on their system, they send the digitally signed emails with the digital signature that comes with smime.p7s file format.

If an email client like Outlook installs an Email Signing certificate and signs an outgoing message, the system will automatically send the smime.p7s file with the outgoing message. For example, in Outlook, a user can find an email signed with a trusted certificate by clicking on the red ribbon. It will look something like this:


how to open smime file When you click on the red ribbon or any other icon, which is an indication of a verified sender, you can see the sender’s validated information with who issued the Email signing certificate. It will look something like this:

digital-signature-valid.png digital signature valid However, people start questioning it when signed messages arrive in other mail hosts, which is the SMIME.p7s file comes as an attachment. It looks like this:

other-email-host.png other email host Here, we have shown the message in the Gmail browser interface. As it does not support .p7s, it is seen as an attachment. However, the server processes the signature and shows the red ribbon is shown to show that the message is safe:

inbox.png inbox So now that we know what is a p7s file, let us address the next question which is whether or not you can open the file.

Can I open an SMIME.p7s file?

If we want to speak technically, you can open a p7s file in Microsoft Outlook, but it is not a file that is really meant or is necessary for a user to be opened. It is present for the email client for authentication of the sender of the secured email message. Typically, there is not really much one gets out of opening the file.

Having said that, if you still insist on opening the file, here is how to do it:

How to Open an SMIME.p7s File?

One can usually find the p7s files in the email messages that include a S/MIME digital signature. They are an indicator that the message is secure and can only be read by the intended recipient. P7s file extension verifies that the email is actually from the person it claims to be from and that the content has not been modified during the transit process.

So if you want to open this file, below are the steps you can follow,

#Step-1: The first step would be to ensure that you have the correct program needed to open a .p7s file. In most recent operating systems, when you install a suitable program, it will automatically result in the correct file association with it. If the file is already present, open the folder which contains the P7S file.

#Step-2: For launching the .p7s file, simply double-click or tap (touchscreen) on the file itself. In case the file does not open, try adjusting the settings of your operating system manually.

For opening the P7s file, depending on your particular operating system, you can install any software mentioned above and let it do the work for you.

#Step-3: Select the software from the list of default applications, select and click ‘Open’.

Though it is not really necessary, if you want to open the file, you have to follow the above-mentioned steps. Most email applications like Apple, Mozilla Thunderbird, and Microsoft Outlook support digital signatures. However, if your email program does not support it, a P7s file appears as an attachment to a digitally signed email message. These emails usually integrate Public-Key Cryptography Standard #7 or PKCS #7 technology to affix encrypted signatures to email messages digitally.

Now, let us discuss who needs an email signing certificate.

Who Needs Email Signing Certificate?

Email and Document Signing Certificates, called CPACs (Comodo Personal Authentication Certificates), are used for emails and certain documents. Signing helps in several ways, such as:

Verifying the identity of the mail’s sender to know that the message is authentic. Alerting you if the document or the email is tampered and it can even block access. Helps to encrypt an email message so that only the intended recipient can read it.


SMIME is the standard used for encrypting an email. Email clients support it and recognize smime.p7s, and verify the contents of an email. But, oftentimes, one might find the smime.p7s file as an attachment, especially if you use other email hosts like Gmail. If that is the case, you need not worry. It is totally fine to trust that email. It simply means that your email host doesn’t support a .p7s file like Outlook and comes as an attachment.

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