Hi DanielHashanth,
However, questions do arise if the signed messages arrive in other mail hosts, in which the SMIME.p7s file is seen as an attachment.
Based on my research, this could be an expected behavior when the signed messages arrive in mail hosts which don’t support digital signatures. Given this, you may tell the external recipients that it's safe to trust the email and there is no need to worry.
Here are some relevant links for your reference:
What is a smime.p7s email attachment? (See the "Other mail hosts" part)
What is a smime.p7s File and How to Open It?
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